Resist composition, method of forming resist pattern and polymeric compound

ABSTRACT

A resist composition including a base component (A) which generates acid upon exposure and exhibits changed solubility in a developing solution under the action of acid, the base component (A) containing a polymeric compound (A1) including a structural unit (a0) represented by general formula (a0-1) shown below, a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid and a structural unit (a6) which generates acid upon exposure (wherein R 1  represents a hydrogen atom, an alkyl group or a halogenated alkyl group; W represents —COO—, —CONH— or a divalent aromatic hydrocarbon group; Y 1  and Y 2  represents a divalent linking group or a single bond; represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′ 2  represents a monovalent aliphatic hydrocarbon group; and R 2  represents an —SO 2 — containing cyclic group).

TECHNICAL FIELD

The present invention relates to a resist composition exhibiting excellent lithography properties, a method of forming a resist pattern using the resist composition, and a polymeric compound useful for a resist composition.

Priority is claimed on Japanese Patent Application No. 2012-066366, filed Mar. 22, 2012, the content of which is incorporated herein by reference.

DESCRIPTION OF RELATED ART

In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions of the resist film become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions of the resist film become insoluble in a developing solution is called a negative-type.

In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.

Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV), and X ray.

Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.

Conventionally, as a resist material that satisfies these conditions, a chemically amplified composition is used, which includes an acid-generator component that generates acid upon exposure and a base material component that exhibits a changed solubility in a developing solution under the action of acid.

As the base component used in a chemically amplified resist composition, a resin (base resin) is generally used.

For example, in the case of forming a positive-tone resist pattern by an alkali developing process using an alkali developing solution as the developing solution, a chemically amplified resist which contains an acid generator and a resin composition that exhibits increased solubility in an alkali developing solution by the action of acid is generally used. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid-generator component, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. Thus, by conducting alkali developing, the unexposed portions remain to form a positive resist pattern.

As the resin component, a resin that exhibits increased polarity by the action of acid is generally used. When the polarity increases, the solubility of the resin in an alkali developing solution is increased, whereas the solubility of the resin in an organic solvent decreases. Therefore, when such a base resin is applied to a solvent developing process using a developing solution containing an organic solvent (organic developing solution) instead of an alkali developing process, the solubility of the exposed portions in an organic developing solution is decreased. As a result, in the solvent developing process, the unexposed portions of the resist film are dissolved and removed by the organic developing solution, and a negative resist pattern in which the exposed portions are remaining is formed. Such a solvent developing process for forming a negative-tone resist composition is sometimes referred to as “negative-tone developing process” (for example, see Patent Document 1).

Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for chemically amplified resist compositions that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2). Here, the term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position.

On the other hand, as acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt acid generators; oxime sulfonate acid generators; diazomethane acid generators; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators. Among these, as acid generators, onium salt acid generators having an onium ion such as a triphenylsulfonium ion as the cation moiety are widely used.

Further, in recent years, the aforementioned resin components which include a structural unit having a sultone ring have been proposed. Conventionally, such structural unit has been suggested to be added for improving the adhesion of the resist composition with the substrate (see, for example, Patent Document 3).

In recent years, a base resin which has an acid generating group that generates acid upon exposure has been proposed. For example, a resin component which has in the structure thereof an acid generating group which generates acid upon exposure and an acid decomposable group which exhibits changed polarity by the action of acid has been proposed (see, for example, Patent Documents 4 to 6). Such a resin component has both the function as an acid generator and the function as a base component, and hence, can compose a chemically amplified resist composition by just one component. That is, when such a resin component is subjected to exposure, acid is generated from the acid-generator group in the structure thereof, and the acid decomposable group is decomposed by the generated acid, thereby forming a polar group such as a carboxy group so as to exhibit increased polarity. When a resin film (resist film) formed using such a resin component is subjected to selective exposure, the polarity of the exposed portions is increased. Thus, by conducting developing by using an alkali developing solution, the exposed portions are dissolved and removed, thereby forming a positive resist pattern.

DOCUMENTS OF RELATED ART Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2009-25707

[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2009-258695

[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2011-158879

[Patent Document 4] Japanese Unexamined Patent Application, First Publication No. Hei 10-221852

[Patent Document 5] Japanese Unexamined Patent Application, First

Publication No. 2006-045311

[Patent Document 6] Japanese Unexamined Patent Application, First Publication No. 2010-095643

SUMMARY OF THE INVENTION

As miniaturization of resists progress, there is still room for improvement in the lithography properties of the conventional resist materials. Further, there were cases where it was difficult to optimize the resin depending on the lithography conditions.

The present invention takes the above circumstances into consideration, with an object of providing a polymeric compound having an acid decomposable group and an acid generating group; a resist composition using the polymeric compound as a base component, and which ca be used to form a fine resist pattern with excellent lithography properties; and a method of forming a resist pattern using the resist composition.

For solving the above-mentioned problems, the present invention employs the following aspects.

Specifically, a first aspect of the present invention is a resist composition including a base component (A) which generates acid upon exposure and exhibits changed solubility in a developing solution under the action of acid, the base component (A) containing a polymeric compound (A1) including a structural unit (a0) represented by general formula (a0-1) shown below, a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid and a structural unit (a6) which generates acid upon exposure.

In the formula, R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂— containing cyclic group.

A second aspect of the present invention is a method of forming a resist pattern, including: using a resist composition of the first aspect to form a resist film on a substrate; conducting exposure of the resist film; and developing the resist film to form a resist pattern.

A third aspect of the present invention is a polymeric compound including a structural unit (a0) represented by general formula (a0-1) shown below, a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid and a structural unit (a6) which generates acid upon exposure.

In the formula, R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂— containing cyclic group.

In the present description and claims, an “alkyl group” includes linear, branched or cyclic, monovalent saturated hydrocarbon, unless otherwise specified.

The term “alkylene group” includes linear, branched or cyclic divalent saturated hydrocarbon, unless otherwise specified.

A “halogenated alkyl group” is a group in which part or all of the hydrogen atoms of an alkyl group is substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

The term “aliphatic” is a relative concept used in relation to the term “aromatic”, and defines a group or compound that has no aromaticity.

The term “structural unit” refers to a monomer unit that contributes to the formation of a polymeric compound (polymer, copolymer).

The term “exposure” is used as a general concept that includes irradiation with any form of radiation.

According to the present invention, there are provided a polymeric compound having an acid decomposable group and an acid generating group; a resist composition using the polymeric compound as a base component, and which ca be used to form a fine resist pattern with excellent lithography properties; and a method of forming a resist pattern using the resist composition.

DETAILED DESCRIPTION OF THE INVENTION

<<Resist Composition>>

The resist composition according to a first aspect of the present invention includes a base component (A) which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid (hereafter, sometimes referred to as “component (A)”).

By virtue of containing the component (A), the resist composition of the present invention has a characteristic of exhibiting changed solubility in a developing solution upon exposure. When a resist film is formed using the resist composition, and the resist film is subjected to a selective exposure, acid is generated from the component (A) at exposed portions, and the generated acid acts on the component (A) to change the solubility of the component (A) in a developing solution. As a result, the solubility of the exposed portions in a developing solution is changed, whereas the solubility of the unexposed portions in a developing solution remain unchanged. Therefore, by subjecting the resist film to development, the exposed portions are dissolved and removed to form a positive-tone resist pattern in the case of a positive resist, whereas the unexposed portions are dissolved and removed to form a negative-tone resist pattern in the case of a negative resist.

In the present specification, a resist composition which forms a positive resist pattern by dissolving and removing the exposed portions is called a positive resist composition, and a resist composition which forms a negative resist pattern by dissolving and removing the unexposed portions is called a negative resist composition.

The resist composition of the present invention may be either a positive resist composition or a negative resist composition. Further, in the formation of a resist pattern, the resist composition of the present invention can be applied to an alkali developing process using an alkali developing solution in the developing treatment, or a solvent developing process using a developing solution containing an organic solvent (organic developing solution) in the developing treatment. The resist composition of the present invention is preferably used in the formation of a positive-tone resist pattern by an alkali developing process and a negative-tone resist pattern by a solvent developing process. In such a case, as the component (A), a base component that exhibits increased solubility in an alkali developing solution (decreased solubility in an organic developing solution) under the action of acid is used.

<Component (A)>

The component (A) used in the resist composition of the present invention is a base component which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid, and contains a resin component (A1) (hereafter, sometimes referred to as “component (A1)”) which includes a structural unit (a0), a structural unit (a1) and a structural unit (a6) described later.

Here, the term “base component” refers to an organic compound capable of forming a film, and is preferably an organic compound having a molecular weight of 500 or more. When the organic compound has a molecular weight of 500 or more, the film-forming ability is improved, and a resist pattern of nano level can be easily formed. The “organic compound having a molecular weight of 500 or more” which can be used as a base component is broadly classified into non-polymers and polymers.

In general, as a non-polymer, any of those which have a molecular weight in the range of 500 to less than 4,000 is used. Hereafter, a non-polymer having a molecular weight in the range of 500 to less than 4,000 is referred to as a low molecular weight compound.

As a polymer, any of those which have a molecular weight of 1,000 or more is generally used. Hereafter, a polymer having a molecular weight of 1,000 or more is referred to as a polymeric compound. With respect to a polymeric compound, the “molecular weight” is the weight average molecular weight in terms of the polystyrene equivalent value determined by gel permeation chromatography (GPC). Hereafter, a polymeric compound is frequently referred to simply as a “resin”.

[Component (A1)]

The component (A) contains a resin component (A1) (hereafter, referred to as component (A1)) which includes a structural unit (a0) represented by general formula (a0-1) shown below, a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid and a structural unit (a6) which generates acid upon exposure.

In the formula, R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂— containing cyclic group.

(Structural Unit (a0))

The structural unit (a0) is a structural unit represented by the aforementioned general formula (a0-1).

In formula (a0-1), R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group for R¹ is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group.

The halogenated alkyl group of 1 to 5 carbon atoms represented by R¹ is a group in which part or all of the hydrogen atoms of the aforementioned alkyl group of 1 to 5 carbon atoms have been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

As R¹, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly desirable in terms of industrial availability.

In formula (a0-1), W represents —COO—, —CONH— or a divalent aromatic hydrocarbon group.

The divalent aromatic hydrocarbon group is a divalent hydrocarbon group having at least one aromatic ring, and may have a substituent. The aromatic ring is not particularly limited, as long as it is a cyclic conjugated compound having (4 n+2)π electrons (wherein n represents 0 or a natural number), and may be either monocyclic or polycyclic. Examples of the aromatic ring include aromatic hydrocarbon rings such as benzene, naphthalene, anthracene and phenanthrene.

As the divalent aromatic hydrocarbon group, an aromatic hydrocarbon group of 6 to 15 carbon atoms can be mentioned.

Specific examples include groups in which 2 hydrogen atoms have been removed from benzene, naphthalene, anthracene, phenanthrene or pyrene, and a phenylene group or a naphthylene group is preferable. These groups may have a substituent described later.

In formula (a0-1), Y¹ and Y² each independently represents a divalent linking group or a single bond. Y¹ and Y² may be the same or different from each other.

As preferable examples of the divalent linking group for Y¹ and Y², a divalent hydrocarbon group which may have a substituent, and a divalent linking group containing a hetero atom can be given.

(Divalent Hydrocarbon Group which may have a Substituent)

The divalent hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

As specific examples of the aliphatic hydrocarbon group, a linear or branched aliphatic hydrocarbon group, and an aliphatic hydrocarbon group containing a ring in the structure thereof can be given.

The linear or branched aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 8, and still more preferably 1 to 5.

As the linear aliphatic hydrocarbon group, a linear alkylene group is preferable. Specific examples thereof include a methylene group [—CH₂—], an ethylene group [—(CH₂)₂—], a trimethylene group [—(CH₂)₃—], a tetramethylene group [—(CH₂)₄—] and a pentamethylene group [—(CH₂)₅—].

As the branched aliphatic hydrocarbon group, branched alkylene groups are preferred, and specific examples include various alkylalkylene groups, including alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)—, and —C(CH₂CH₃)₂—; alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, and —C(CH₂CH₃)₂—CH₂—; alkyltrimethylene groups such as —CH(CH₃)CH₂CH₂—, and —CH₂CH(CH₃)CH₂—; and alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—, and —CH₂CH(CH₃)CH₂CH₂—. As the alkyl group within the alkylalkylene group, a linear alkyl group of 1 to 5 carbon atoms is preferable.

The linear or branched aliphatic hydrocarbon group may or may not have a substituent (a group or atom other than hydrogen) which substitutes the hydrogen atom. Examples of the substituent include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxo group (═O).

As examples of the hydrocarbon group containing a ring in the structure thereof, a cyclic aliphatic hydrocarbon group containing a hetero atom in the ring structure thereof and may have a substituent (a group in which two hydrogen atoms have been removed from an aliphatic hydrocarbon ring), a group in which the cyclic aliphatic hydrocarbon group is bonded to the terminal of the aforementioned chain-like aliphatic hydrocarbon group, and a group in which the cyclic aliphatic group is interposed within the aforementioned linear or branched aliphatic hydrocarbon group, can be given. As the linear or branched aliphatic hydrocarbon group, the same groups as those described above can be used.

The cyclic aliphatic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms.

The cyclic aliphatic hydrocarbon group may be polycyclic or monocyclic. As the monocyclic aliphatic hydrocarbon group, a group in which 2 hydrogen atoms have been removed from a monocycloalkane is preferable. The monocycloalkane preferably has 3 to 6 carbon atoms, and specific examples thereof include cyclopentane and cyclohexane. As the polycyclic aliphatic hydrocarbon group, a group in which two hydrogen atoms have been removed from a polycycloalkane is preferable, and the polycyclic group preferably has 7 to 12 carbon atoms. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The cyclic aliphatic hydrocarbon group may or may not have a substituent (a group or atom other than hydrogen) which substitutes the hydrogen atom. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group and an oxo group (═O).

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

The cyclic aliphatic hydrocarbon group may have part of the carbon atoms constituting the ring structure thereof substituted with a substituent containing a hetero atom. As the substituent containing a hetero atom, —O—, —C(═O)—O—, —S—, —S(═O)₂— or —S(═O)₂—O— is preferable.

The aromatic group for the divalent hydrocarbon group is the same as defined for the aforementioned aromatic hydrocarbon group for W, and a phenylene group or a naphthylene group is preferable.

The aromatic group may or may not have a substituent. For example, the hydrogen atom bonded to the aromatic ring within the aromatic group may be substituted with a substituent. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group and an oxo group (═O).

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

(Divalent Linking Group Containing a hetero Atom)

With respect to a “divalent linking group containing a hetero atom”, a hetero atom is an atom other than carbon and hydrogen, and examples thereof include an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom and a silicon atom.

Specific examples of the divalent linking group containing a hetero atom include non-hydrocarbon linking groups such as —O—, —C(═O)—, —C(═O)—O—, —O—C(═O)—O—, —S—, —S(═O)₂—, —S(═O)₂—O—, —NH—, —NH—C(═O)—, —NH—C(═NH)—, ═N— and —SiH₂—O—; and a combination of any one of these non-hydrocarbon linking groups with a divalent hydrocarbon group. The divalent hydrocarbon group is the same as defined for the aforementioned divalent hydrocarbon group which may have a substituent. As the combination, it is preferable to select from an alkylene group, a phenylene group, a naphthylene group, —O—, —C(═O)— and —C(═O)—O—.

Among these, as Y¹ and Y², a single bond or an arylene group such as a phenylene group or a naphthylene group is preferable.

The alkyl group of 1 to 6 carbon atoms for R′¹ is preferably the aforementioned alkyl group of 1 to 5 carbon atoms, a cyclopentyl group or a cyclohexyl group. As R′¹, a hydrogen atom, a methyl group or an ethyl group is preferable, and a hydrogen atom is more preferable.

The aliphatic hydrocarbon group for R′² may be either a saturated aliphatic hydrocarbon group, or an unsaturated aliphatic hydrocarbon group. Further, the aliphatic hydrocarbon group may be linear, branched or cyclic. Among these, a linear or branched, saturated aliphatic hydrocarbon group is preferable.

In the aliphatic hydrocarbon group for R′², part of the carbon atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom, or part or all of the hydrogen atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom.

As the “hetero atom” for R′², there is no particular limitation as long as it is an atom other than carbon and hydrogen.

Examples of the halogen atom include a fluorine atom, a chlorine atom, an iodine atom and a bromine atom.

The substituent group containing a hetero atom may consist of a hetero atom, or may be a group containing a group or atom other than a hetero atom.

Specific examples of the substituent group for substituting part of the carbon atoms include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (the H may be replaced with a substituent such as an alkyl group or an acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—. When the aliphatic hydrocarbon group is cyclic, the aliphatic hydrocarbon group may contain any of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of the hydrogen atoms include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group.

The aforementioned alkoxy group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Example of the aforementioned halogenated alkyl group includes a group in which part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms.

As the aliphatic hydrocarbon group, a linear, branched or cyclic, saturated hydrocarbon group is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 5. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group. As the cyclic saturated hydrocarbon group (alkyl group), a cyclopentyl group or a cyclohexyl group is preferable.

Examples of the substituent for R′² include a halogen atom, an oxy group (═O), a cyano group, an alkyl group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, —C(═O)—O—R⁷″, —O—C(═O)—R⁸″, —O—R⁹″, —NH— and an aryl group.

R⁷″, R⁸″ and R⁹″ each independently represents a hydrogen atom or a hydrocarbon group.

Examples of the halogen atom as the substituent include a fluorine atom, an iodine atom and a bromine atom, and a fluorine atom is preferable.

In formula (a0-1), as R′², a linear or cyclic alkyl group is preferable.

In formula (a0-1), as R′², a linear or cyclic alkyl group is preferable. In the case where and R′² represent an alkyl group, and R′² may be mutually bonded to form a ring.

In general formula (a0-1), R² represents a cyclic group containing —SO₂— in the ring structure thereof More specifically, R² is a cyclic group in which the sulfur atom (S) within the —SO₂— group forms part of the ring skeleton thereof.

The cyclic group for R² refers to a cyclic group including a ring that contains —SO₂— within the ring skeleton thereof, and this ring is counted as the first ring. A cyclic group in which the only ring structure is the ring that contains —SO₂— in the ring skeleton thereof is referred to as a monocyclic group, and a group containing other ring structures is described as a polycyclic group regardless of the structure of the other rings. The cyclic group for R² may be either a monocyclic group or a polycyclic group.

As R², a cyclic group containing —O—SO₂— within the ring skeleton thereof, i.e., a cyclic group containing a sultone ring in which —O—S— within the —O—SO₂— group forms part of the ring skeleton thereof is particularly desirable.

The cyclic group for R² preferably has 3 to 30 carbon atoms, more preferably 4 to 20, still more preferably 4 to 15, and most preferably 4 to 12.

Herein, the number of carbon atoms refers to the number of carbon atoms constituting the ring skeleton, excluding the number of carbon atoms within a substituent.

The cyclic group for R² may be either an aliphatic cyclic group or an aromatic cyclic group.

An aliphatic cyclic group is preferable.

Examples of aliphatic cyclic groups for R² include the aforementioned cyclic aliphatic hydrocarbon groups in which part of the carbon atoms constituting the ring skeleton thereof has been substituted with —SO₂— or —O—SO₂—.

More specifically, examples of monocyclic groups include a monocycloalkane in which one hydrogen atom have been removed therefrom and a —CH₂— group constituting the ring skeleton thereof has been substituted with —SO₂—; and a monocycloalkane in which one hydrogen atom have been removed therefrom and a —CH₂—CH₂— group constituting the ring skeleton thereof has been substituted with —O—SO₂—. Examples of polycyclic groups include a polycycloalkane (a bicycloalkane, a tricycloalkane, a tetracycloalkane or the like) in which one hydrogen atom have been removed therefrom and a —CH₂— group constituting the ring skeleton thereof has been substituted with —SO₂—; and a polycycloalkane in which one hydrogen atom have been removed therefrom and a —CH₂—CH₂— group constituting the ring skeleton thereof has been substituted with —O—SO₂—.

The cyclic group for R² may have a substituent. Examples of the substituent include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), —COOR″, —OC(═O)R″, a hydroxyalkyl group and a cyano group.

The alkyl group for the substituent is preferably an alkyl group of 1 to 6 carbon atoms. Further, the alkyl group is preferably a linear alkyl group or a branched alkyl group. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group and a hexyl group. Among these, a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

As the alkoxy group for the substituent, an alkoxy group of 1 to 6 carbon atoms is preferable. Further, the alkoxy group is preferably a linear or branched alkoxy group. Specific examples of the alkoxy group include the aforementioned alkyl groups for the substituent having an oxygen atom (—O—) bonded thereto.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

As examples of the halogenated alkyl group for the substituent, groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups for the substituent have been substituted with the aforementioned halogen atoms can be given. As the halogenated alkyl group, a fluorinated alkyl group is preferable, and a perfluoroalkyl group is particularly desirable.

In the —COOR″ group and the —OC(═O)R″ group, R″ represents a hydrogen atom or a linear, branched or cyclic alkyl group of 1 to 15 carbon atoms.

When R″ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1 to 5 carbon atoms, and most preferably a methyl group or an ethyl group.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The hydroxyalkyl group for the substituent preferably has 1 to 6 carbon atoms, and specific examples thereof include the aforementioned alkyl groups for the substituent in which at least one hydrogen atom has been substituted with a hydroxy group.

More specific examples of R² include groups represented by general formulas (3-1) to (3-4) shown below.

In the formulas, A′ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; a represents an integer of 0 to 2; and R⁸ represents an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyl group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group.

In general formulas (3-1) to (3-4) above, A′ represents an oxygen atom (—O—), a sulfur atom (—S—) or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom.

As the alkylene group of 1 to 5 carbon atoms represented by A′, a linear or branched alkylene group is preferable, and examples thereof include a methylene group, an ethylene group, an n-propylene group and an isopropylene group.

Examples of alkylene groups that contain an oxygen atom or a sulfur atom include the aforementioned alkylene groups in which —O— or —S— is bonded to the terminal of the alkylene group or present between the carbon atoms of the alkylene group. Specific examples of such alkylene groups include —O—CH₂—, —CH₂—O—CH₂—, —S—CH₂—, —CH₂—S—CH₂—.

As A′, an alkylene group of 1 to 5 carbon atoms or —O— is preferable, more preferably an alkylene group of 1 to 5 carbon atoms, and most preferably a methylene group.

a represents an integer of 0 to 2, and is most preferably 0.

When a is 2, the plurality of R⁸ may be the same or different from each other.

As the alkyl group, alkoxy group, halogenated alkyl group, halogenated alkyl group, hydroxyl group, —COOR″, —OC(═O)R″, hydroxyalkyl group and cyano group for R⁸, the same alkyl groups, alkoxy groups, halogenated alkyl groups, halogenated alkyl groups, hydroxyl groups, —COOR″, —OC(═O)R″, hydroxyalkyl groups and cyano groups as those described above as the substituent which the cyclic group for R³ may have can be used.

Specific examples of the cyclic groups represented by general formulas (3-1) to (3-4) are shown below.

In the formulas shown below, “Ac” represents an acetyl group.

Among the examples shown above, as R², a group represented by general formula (3-1), (3-3) or (3-4) shown below is preferable, and a cyclic group represented by general formula (3-1) shown below is particularly desirable.

More specifically, as R², it is preferable to use at least one cyclic group selected from the group consisting of groups represented by chemical formulas (3-1-1), (3-1-18), (3-3-1) and (3-4-1) above, and a group represented by the aforementioned chemical formula (3-1-1) is particularly desirable.

In the present invention, as the structural unit (a0), a structural unit represented by any one of general formulae (a0-1-11) to (a0-1-18) shown below is particularly desirable.

In the formulae, R¹ and A′ are the same as defined above.

A′ is preferably a methylene group, an oxygen atom (—O—) or a sulfur atom (—S—).

As the structural unit (a0-1), one type of structural unit may be used alone, or two or more types of structural units may be used in combination.

In terms of achieving excellent properties with respect to MEF, the shape of a formed resist pattern (e.g., the rectangularity of a line pattern, the circularity of a hole pattern, and the like), critical dimension uniformity (CDU), line width roughness (LWR) and the like in the formation of a resist pattern using a resist composition containing the component (A1), the amount of the structural unit (a0) within the component (A1), based on the combined total of all structural units constituting the component (A1) is preferably 1 to 60 mol %, more preferably 5 to 55 mol %, and still more preferably 10 to 50 mol %.

(Structural Unit (a6))

The structural unit (a6) preferably has a group represented by general formula (a6-0-1) shown below or a group represented by general formula (a6-0-2) shown below. That is, the structural unit (a6) is preferably a structural unit having a group represented by general formula (a6-0-1) shown below (hereafter, this structural unit is referred to as “structural unit (a6-0-1)”) or a structural unit having a group represented by general formula (a6-0-2) shown below (hereafter, this structural unit is referred to as “structural unit (a6-0-2)”).

In the formulae, Q¹ and Q² each independently represents a single bond or a divalent linking group; R³, R⁴ and R⁵ each independently represents an organic group, provided that R⁴ and R⁵ may be mutually bonded to form a ring with the sulfur atom in the formula; V⁻ represent a counteranion; A⁻ represents an organic group containing an anion; and M^(m+) represents an organic cation having a valency of m, wherein m represents an integer of 1 to 3.

In formula (a6-0-1), Q¹ represents a single bond or a divalent linking group.

The divalent linking group for Q¹ is the same as defined for the divalent linking group for Y¹ and Y² in the aforementioned formula (a0-1). In the present invention, Q¹ preferably represents an ester bond [—C(═O)—O—], an ether bond (—O—), an alkylene group, a combination of these, or a single bond.

In formula (a6-0-1), R³, R⁴ and R⁵ each independently represents an organic group, provided that R⁴ and R⁵ may be mutually bonded to form a ring with the sulfur atom in the formula.

The organic group for R³ to R⁵ refers to a group containing a carbon atom, and may include atoms other than carbon (e.g., a hydrogen atom, an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom (such as a fluorine atom and a chlorine atom) and the like).

Specific examples of the organic group for R³ include an alkylene group which may have substituent, and arylene group which may have substituent. Among these, an alkylene group which may have substituent is preferable.

Examples of the alkylene group for R³ which may have substituent include an unsubstituted alkylene group, and a substituted alkylene group in which part or all of the hydrogen atoms within an unsubstituted alkylene group has been substituted with a hydrogen atom.

The unsubstituted alkylene group may be linear, branched or cyclic. In terms of superiority in resolution, an alkylene group of 1 to 10 carbon atoms is preferable, and an alkylene group of 1 to 5 carbon atoms is more preferable. Specific examples include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, an isobutylene group, an n-pentylene, a cyclopentylene group, a hexylene group, a cyclohexylene group, a nonylene group and a decylene group.

Examples of the substituent for the substituted alkylene group include a halogen atom, an oxy group (═O), a cyano group, an alkyl group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, —C(═O)—O—R⁷″, —O—C(═O)—R⁸″, —O—R⁹″ and an aryl group. R⁷″, R⁸″ and R⁹″ each independently represents a hydrogen atom or a hydrocarbon group.

Examples of the halogen atom as the substituent include a fluorine atom, an iodine atom and a bromine atom, and a fluorine atom is preferable.

The alkyl group as the substituent for the substituted alkylene group may be linear, branched or cyclic. The number of carbon atoms thereof is preferably 1 to 30.

Among these, the linear alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched alkyl group preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group.

The cyclic alkyl group may be either a monocyclic group or a polycyclic group. The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. As the aliphatic cyclic group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The cyclic alkyl group is preferably a polycyclic group, more preferably a group in which one or more hydrogen atoms have been removed from a polycycloalkane, and most preferably a group in which one or more hydrogen atoms have been removed from adamantane.

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

Examples of alkoxyalkyloxy groups as the substituent for the substituted alkylene group include groups represented by a general formula shown below:

general formula: —O—C(R⁴⁷)(R⁴⁸)—O—R⁴⁹ (in the formula, each of R⁴⁷ and R⁴⁸ independently represent a hydrogen atom or a linear or branched alkyl group; and R⁴⁹ represents an alkyl group).

The alkyl group for R⁴⁷ and R⁴⁸ preferably has 1 to 5 carbon atoms, and may be either linear or branched. As the alkyl group, an ethyl group or a methyl group is preferable, and a methyl group is most preferable.

It is preferable that at least one of R⁴⁷ and R⁴⁸ be a hydrogen atom. It is particularly desirable that at least one of R⁴⁷ and R⁴⁸ be a hydrogen atom, and the other be a hydrogen atom or a methyl group.

The alkyl group for R⁴⁹ preferably has 1 to 15 carbon atoms, and may be linear, branched or cyclic.

The linear or branched alkyl group for R⁴⁹ preferably has 1 to 5 carbon atoms. Examples thereof include a methyl group, an ethyl group, a propyl group, an n-butyl group and a tert-butyl group.

The cyclic alkyl group for R⁴⁹ preferably has 4 to 15 carbon atoms, more preferably 4 to 12, and most preferably 5 to 10. Specific examples thereof include groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, and which may or may not be substituted with an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group. Examples of the monocycloalkane include cyclopentane and cyclohexane. Examples of polycycloalkanes include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane. Among these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable.

Examples of alkoxycarbonylalkyloxy groups as the substituent for the substituted alkylene group include groups represented by a general formula shown below:

a group represented by a general formula —O—R⁵⁰ —C(═O)—O—R⁵⁶ (in the formula, R⁵⁰ represents a linear or branched alkylene group; and R⁵⁶ represents a tertiary alkyl group.)

The linear or branched alkylene group for R⁵⁰ preferably has 1 to 5 carbon atoms, and examples thereof include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group and a 1,1-dimethylethylene group.

Examples of the tertiary alkyl group for R⁵⁶ include a 2-methyl-2-adamantyl group, a 2-(2-propyl)-2-adamantyl group, a 2-ethyl-2-adamantyl group, a 1-methyl-1-cyclopentyl group, a 1-ethyl-1-cyclopentyl group, a 1-methyl-1-cyclohexyl group, a 1-ethyl-1-cyclohexyl group, a 1-(1-adamantyl)-1-methylethyl group, a 1-(1-adamantyl)-1-methylpropyl group, a 1-(1-adamantyl)-1-methylbutyl group, a 1-(1-adamantyl)-1-methylpentyl group, a 1-(1-cyclopentyl)-1-methylethyl group, a 1-(1-cyclopentyl)-1-methylpropyl group, a 1-(1-cyclopentyl)-1-methylbutyl group, a 1-(1-cyclopentyl)-1-methylpentyl group, a 1-(1-cyclohexyl)-1-methylethyl group, a 1-(1-cyclohexyl)-1-methylpropyl group, a 1-(1-cyclohexyl)-1-methylbutyl group, a 1-(1-cyclohexyl)-1-methylpentyl group, a tert-butyl group, a tert-pentyl group and a tert-hexyl group.

Further, a group in which R⁵⁶ in the group represented by the aforementioned general formula: —O—R⁵⁰—C(═O)—O—R⁵⁶ has been substituted with R⁵⁶′ can also be mentioned. R⁵⁶′ represents a hydrogen atom, an alkyl group, a fluorinated alkyl group or an aliphatic cyclic group which may contain a hetero atom.

The alkyl group for R⁵⁶′ is the same as defined for the alkyl group for the aforementioned R⁴⁹.

Examples of the fluorinated alkyl group for R⁵⁶′ include groups in which part or all of the hydrogen atoms within the alkyl group for R⁴⁹ has been substituted with a fluorine atom.

Examples of the aliphatic cyclic group for R⁵⁶′ which may contain a hetero atom include an aliphatic cyclic group which does not contain a hetero atom, an aliphatic cyclic group containing a hetero atom in the ring structure, and an aliphatic cyclic group in which a hydrogen atom has been substituted with a hetero atom.

As an aliphatic cyclic group for R⁵⁶′ which does not contain a hetero atom, a group in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, a tricycloalkane or a tetracycloalkane can be mentioned. Examples of the monocycloalkane include cyclopentane and cyclohexane. Examples of polycycloalkanes include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane. Among these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable.

Specific examples of the aliphatic cyclic group for R⁵⁶′ containing a hetero atom in the ring structure include groups represented by formulas (L1) to (L5) and (S1) to (S4) described later.

As the aliphatic cyclic group for R⁵⁶′ in which a hydrogen atom has been substituted with a hetero atom, an aliphatic cyclic group in which a hydrogen atom has been substituted with an oxo group (═O) can be mentioned.

As the aliphatic cyclic group for R⁵⁶′ in which a hydrogen atom has been substituted with a hetero atom, an aliphatic cyclic group in which a hydrogen atom has been substituted with an oxo group (═O) can be mentioned.

R⁷″ within —C(═O)—O—R⁷″ represents a hydrogen atom or a hydrocarbon group.

The hydrocarbon group for R⁷″ may be either an aliphatic hydrocarbon group, or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group.

The saturated hydrocarbon group for R⁷″ may be linear, branched or cyclic, or a combination thereof.

The linear or branched saturated hydrocarbon group preferably has 1 to 25 carbon atoms, more preferably 1 to 15, and still more preferably 4 to 10.

Examples of the linear, saturated hydrocarbon group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group and a decyl group.

Examples of the branched, saturated hydrocarbon group include the tertiary alkyl groups described for R⁵⁶. Examples of branched, saturated hydrocarbon groups other than tertiary alkyl groups include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group.

The linear or branched, saturated hydrocarbon group may have a substituent. Examples of the substituent include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxo group (═O), a cyano group and a carboxy group.

The alkoxy group as the substituent for the linear or branched saturated hydrocarbon group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group or a tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the linear or branched, saturated alkyl group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Example of the halogenated alkyl group as the substituent for the linear or branched, saturated hydrocarbon group includes a group in which part or all of the hydrogen atoms within the aforementioned linear or branched, saturated hydrocarbon group have been substituted with the aforementioned halogen atoms.

The cyclic, saturated hydrocarbon group for R⁷″ is preferably 3 to 20. The cyclic saturated hydrocarbon group may be either a polycyclic group or a monocyclic group, and examples thereof include groups in which one hydrogen atom has been removed from a monocycloalkane, and groups in which one hydrogen atom has been removed from a polycycloalkane (e.g., a bicycloalkane, a tricycloalkane or a tetracycloalkane). More specific examples include groups in which one hydrogen atom has been removed from a monocycloalkane such as cyclopentane, cyclohexane, cycloheptane or cyclooctane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The cyclic, saturated hydrocarbon group may have a substituent. For example, part of the carbon atoms constituting the ring within the cyclic alkyl group may be substituted with a hetero atom, or a hydrogen atom bonded to the ring within the cyclic alkyl group may be substituted with a substituent.

In the former example, a heterocycloalkane in which part of the carbon atoms constituting the ring within the aforementioned monocycloalkane or polycycloalkane has been substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom, and one hydrogen atom has been removed therefrom, can be used. Further, the ring may contain an ester bond (—C(═O)—O—). More specific examples include a lactone-containing monocyclic group, such as a group in which one hydrogen atom has been removed from γ-butyrolactone; and a lactone-containing polycyclic group, such as a group in which one hydrogen atom has been removed from a bicycloalkane, tricycloalkane or tetracycloalkane containing a lactone ring.

In the latter example, as the substituent, the same substituent groups as those for the aforementioned linear or branched alkyl group, or an alkyl group of 1 to 5 carbon atoms can be used.

The saturated hydrocarbon group for R⁷″ may be a combination of a linear or branched, saturated hydrocarbon group with a cyclic, saturated hydrocarbon group.

Examples of the combination of a linear or branched, saturated hydrocarbon group with a cyclic, saturated hydrocarbon group include a linear or branched, saturated hydrocarbon group having a cyclic, saturated hydrocarbon group as a substituent bonded thereto; and a cyclic, saturated hydrocarbon group having a linear or branched, saturated hydrocarbon group bonded thereto.

The aliphatic unsaturated hydrocarbon group for R⁷″ is preferably linear or branched. Examples of linear aliphatic unsaturated hydrocarbon groups include a vinyl group, a propenyl group (an ally! group) and a butynyl group. Examples of branched aliphatic unsaturated hydrocarbon groups include a 1-methylpropenyl group and a 2-methylpropenyl group. The aforementioned linear or branched, aliphatic unsaturated hydrocarbon group may have a substituent. Examples of substituents include the same substituents as those which the aforementioned linear or branched alkyl group may have.

The aromatic hydrocarbon group for R⁷″ is a monovalent hydrocarbon group having at least one aromatic ring, and may have a substituent.

The aromatic ring is not particularly limited, as long as it is a cyclic conjugated compound having (4 n+2) it electrons (wherein n represents 0 or a natural number), and may be either monocyclic or polycyclic. The aromatic ring preferably has 5 to 30 carbon atoms, more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group. Examples of the aromatic ring include aromatic hydrocarbon rings, such as benzene, naphthalene, anthracene and phenanthrene; and aromatic hetero rings in which part of the carbon atoms constituting the aforementioned aromatic hydrocarbon rings has been substituted with a hetero atom. Examples of the hetero atom within the aromatic hetero rings include an oxygen atom, a sulfur atom and a nitrogen atom. Specific examples of the aromatic hetero ring include a pyridine ring and a thiophene ring.

Specific examples of the aromatic hydrocarbon group include a group in which one hydrogen atom has been removed from the aforementioned aromatic hydrocarbon ring or aromatic hetero ring (aryl group or heteroaryl group); and a group in which one hydrogen atom of the aforementioned aromatic hydrocarbon ring or aromatic hetero ring has been substituted with an alkylene group (an arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group, or a heteroarylalkyl group). The alkylene group which substitutes the hydrogen atom of the aforementioned aromatic hydrocarbon ring or the aromatic hetero ring preferably has 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms, and most preferably 1 carbon atom.

The aromatic hydrocarbon group may or may not have a substituent. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group and an oxo group (═O).

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

Among the aforementioned examples, as R⁷″, in terms of improvement in lithography properties and shape of the resist pattern, a hydrogen atom, a saturated hydrocarbon group or an aliphatic unsaturated hydrocarbon group is preferable, and a hydrogen atom, a linear or branched, saturated hydrocarbon group of 1 to 15 carbon atoms or a cyclic saturated hydrocarbon group of 3 to 20 carbon atoms is more preferable.

R^(R)″ within —O—C(═O)—R⁸″ represents a hydrogen atom or a hydrocarbon group.

As R⁸″, the same groups as those described above for R⁷″ can be used. Among the aforementioned examples, in terms of improvement in lithography properties and shape of the resist pattern, a hydrogen atom, a saturated hydrocarbon group or an aliphatic unsaturated hydrocarbon group is preferable, and a hydrogen atom, a linear or branched, saturated hydrocarbon group of 1 to 15 carbon atoms or a cyclic saturated hydrocarbon group of 3 to 20 carbon atoms is more preferable.

R⁹″ within —O—R⁹″ represents a hydrogen atom or a hydrocarbon group.

As R⁹″, the same groups as those described above for R⁷″ can be used. Among the aforementioned examples, in terms of improvement in lithography properties and shape of the resist pattern, a hydrogen atom, a saturated hydrocarbon group or an aliphatic unsaturated hydrocarbon group is preferable, and a hydrogen atom, a linear or branched, saturated hydrocarbon group of 1 to 15 carbon atoms or a cyclic saturated hydrocarbon group of 3 to 20 carbon atoms is more preferable.

—O—R⁹″ as the substituent is preferably a hydroxy group, an alkoxy group having 1 to 5 carbon atoms, and a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group or a tert-butoxy group is particularly desirable.

The aryl group as the substituent for the aforementioned substituted alkylene group is preferably an aryl group having 6 to 10 carbon atoms because it can be synthesized at a low cost. Specific examples thereof include a phenyl group and a naphthyl group.

The aryl group as the substituent may have a substituent. Examples of substituents include the same substituents as those which the aromatic hydrocarbon group for R⁷″ may have.

In formula (a6-0-1), examples of the arylene group for R³ which may have substituent include an unsubstituted arylene group of 6 to 20 carbon atoms; and a substituted arylene group in which part or all of the hydrogen atoms within an unsubstituted arylene group has been substituted with a hydrogen atom.

The unsubstituted arylene group is preferably an arylene group having 6 to 10 carbon atoms because it can be synthesized at a low cost. Specific examples thereof include a phenylene group and a naphthylene group.

As specific examples of the substituent for the substituted arylene group, the same groups as those described above for the substituent of the aforementioned substituted alkylene group can be mentioned. More specifically, among the substituents for the substituted alkylene group, a halogen atom, an oxo group (═O), a cyano group, an alkyl group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, —C(═O)—O—R⁷″, —O—C(═O)—R⁸″ and —O—R⁹″ (provided that R⁷″, R⁸″ and R⁹″ each independently represent a hydrogen atom, a saturated hydrocarbon group or an aliphatic, unsaturated hydrocarbon group) can be mentioned.

In formula (a6-0-1), the organic group for R⁴ and R⁵ is not limited, and examples thereof include an aryl group which may have a substituent, an alkyl group which may have a substituent, and an alkenyl group which may have a substituent.

Examples of the aryl group for R⁴ and R⁵ which may have a substituent include an unsubstituted aryl group of 6 to 20 carbon atoms; and a substituted aryl group in which part or all of the hydrogen atoms have been substituted with a substituent.

The unsubstituted aryl group is preferably an aryl group having 6 to 10 carbon atoms because it can be synthesized at a low cost. Specific examples thereof include a phenyl group and a naphthyl group.

As examples of the substituent for the substituted aryl group, the same substituents as those described above for the substituent of the aforementioned substituted arylene group can be mentioned.

Examples of the alkyl group for R⁴ and R⁵ include an unsubstituted alkyl group; and a substituted alkyl group in which part or all of the hydrogen atoms within an unsubstituted alkyl group has been substituted with a hydrogen atom.

The unsubstituted alkyl group may be linear, branched or cyclic. In terms of superiority in resolution, an alkyl group of 1 to 10 carbon atoms is preferable, and an alkyl group of 1 to 5 carbon atoms is more preferable. Specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an n-pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a nonyl group and a decyl group.

As examples of the substituent for the substituted alkyl group, the same groups as those described above as the substituent of the substituted alkylene group for R³ can be mentioned.

Examples of the alkenyl group for R⁴ and R⁵ include an unsubstituted alkenyl group; and a substituted alkenyl group in which part or all of the hydrogen atoms within an unsubstituted alkenyl group has been substituted with a hydrogen atom.

The unsubstituted alkenyl group is preferably linear or branched. Further, the alkenyl group preferably has 2 to 10 carbon atoms, more preferably 2 to 5, and still more preferably 2 to 4. Specific examples thereof include a vinyl group, a propenyl group (an allyl group), a butynyl group, a 1-methylpropenyl group and a 2-methylpropenyl group.

As examples of the substituent for the substituted alkenyl group, the same groups as those described above as the substituent of the substituted alkylene group for R³ can be mentioned.

In formula (a6-0-1), R⁴ and R⁵ may be mutually bonded to form a ring with the sulfur atom in the formula. The ring may be saturated or unsaturated. Further, the ring may be monocyclic or polycyclic. For example, in the case where either one or both of R⁴ and R¹ forming a ring represents a cyclic group (a cyclic alkyl group or an aryl group), R⁴ and R⁵ are bonded to form a polycyclic ring (condensed ring).

The ring containing the sulfur atom in the skeleton thereof is preferably a 3 to 10-membered ring, and most preferably a 5 to 7-membered ring.

The ring may contain a hetero atom other than the sulfur atom bonded to R⁴ and R⁵ which constitutes the ring skeleton. Examples of the hetero atom include an oxygen atom and a nitrogen atom.

Specific examples of the ring formed include a thiophene ring, a thiazole ring, a benzothiophene ring, a thianthrene ring, a benzothiophene ring, a dibenzothiophene ring, a 9H-thioxanthene ring, a thioxanthone ring, a phenoxathiin ring, a tetrahydrothiophenium ring, and a tetrahydrothiopyranium ring.

In formula (a6-0-1), V⁻ represents a counteranion.

As the counteranion for V⁻, there is no particular limitation, and any of those conventionally known as anion moiety for an onium salt acid generator can be appropriately selected for use.

Specific examples of V⁻ include anions represented by general formula: “R⁴″SO₃ ⁻(R⁴″ represents a linear, branched or cyclic alkyl group which may have a substituent, a halogenated alkyl group, an aryl group or an alkenyl group)”.

In the aforementioned general formula “R⁴″SO₃ ⁻”, R⁴″ represents a linear, branched or cyclic alkyl group which may have a substituent, a halogenated alkyl group, an aryl group or an alkenyl group.

The linear or branched alkyl group for the aforementioned R⁴″ preferably has 1 to 10 carbon atoms, more preferably 1 to 8, and most preferably 1 to 4.

The cyclic alkyl group for the aforementioned R⁴″ preferably has 4 to 15 carbon atoms, more preferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms.

When R⁴″ represents an alkyl group, examples of “R⁴″SO₃ ⁻” include alkylsulfonates, such as methanesulfonate, n-propanesulfonate, n-butanesulfonate, n-octanesulfonate, 1-adamantanesulfonate, 2-norbornanesulfonate and d-camphor-10-sulfonate.

The halogenated alkyl group for the aforementioned R⁴″ is an alkyl group in which part or all of the hydrogen atoms thereof have been substituted with a halogen atom. The alkyl group preferably has 1 to 5 carbon atoms, and is preferably a linear or branched alkyl group, and more preferably a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a tert-pentyl group or an isopentyl group. Examples of the halogen atom which substitutes the hydrogen atoms include a fluorine atom, a chlorine atom, an iodine atom and a bromine atom.

In the halogenated alkyl group, it is preferable that 50 to 100% of all hydrogen atoms within the alkyl group (prior to halogenation) have been substituted with a halogen atom, and it is preferable that all hydrogen atoms have been substituted with a halogen atom.

As the halogenated alkyl group, a fluorinated alkyl group is preferable. The fluorinated alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms.

Further, the fluorination ratio of the fluorinated alkyl group is preferably from 10 to 100%, more preferably from 50 to 100%, and it is most preferable that all hydrogen atoms are substituted with fluorine atoms because the acid strength increases.

Specific examples of such fluorinated alkyl groups include a trifluoromethyl group, a heptafluoro-n-propyl group and a nonafluoro-n-butyl group.

The aryl group for R⁴″ is preferably an aryl group of 6 to 20 carbon atoms.

The alkenyl group for R⁴″ is preferably an alkenyl group of 2 to 10 carbon atoms.

With respect to R⁴″, the expression “may have a substituent” means that part of or all of the hydrogen atoms within the aforementioned linear, branched or cyclic alkyl group, halogenated alkyl group, aryl group or alkenyl group may be substituted with substituents (atoms other than hydrogen atoms, or groups).

R⁴″ may have one substituent, or two or more substituents.

Examples of the substituent include a halogen atom, a hetero atom, an alkyl group, and a group represented by the formula X³-Q′- (in the formula, Q′ represents a divalent linking group containing an oxygen atom; and X³ represents a hydrocarbon group of 3 to 30 carbon atoms which may have a substituent).

Examples of halogen atoms and alkyl groups include the same halogen atoms and alkyl groups as those described above with respect to the halogenated alkyl group for R⁴″.

Examples of hetero atoms include an oxygen atom, a nitrogen atom, and a sulfur atom.

In the group represented by formula X³-Q′-, Q′ represents a divalent linking group containing an oxygen atom.

Q′ may contain an atom other than an oxygen atom. Examples of atoms other than oxygen include a carbon atom, a hydrogen atom, a sulfur atom and a nitrogen atom.

Examples of divalent linking groups containing an oxygen atom include non-hydrocarbon, oxygen atom-containing linking groups such as an oxygen atom (an ether bond; —O—), an ester bond (—C(═O)—O—), an amido bond (—C(═O)—NH—), a carbonyl group (—C(═O)—) and a carbonate bond (—O—C(═O)—O—); and combinations of the aforementioned non-hydrocarbon, hetero atom-containing linking groups with an alkylene group. Furthermore, the combinations may have a sulfonyl group (—SO₂—) bonded thereto.

Specific examples of such combinations include —R⁹¹—O—, —R⁹²—O—C(═O)—, —C(═O)—O—R⁹³—O—C(═O)—, —SO₂—O—R⁹⁴—O—C(═O)—, and —R⁹′—SO₂—O—R⁹⁴—O——C(═O)— (in the formula, R⁹¹ to R⁹⁵ independently represents an alkylene group).

The alkylene group for R⁹¹ to R⁹⁵ is preferably a linear or branched alkylene group, and preferably has 1 to 12 carbon atoms, more preferably 1 to 5, and most preferably 1 to 3.

Specific examples of alkylene groups include a methylene group [—CH₂—]; alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)— and —C(CH₂CH₃)₂—; an ethylene group [—CH₂CH₂—]; alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂— and —CH(CH₂CH₃)CH₂—; a trimethylene group (n-propylene group) [—CH₂CH₂CH₂—]; alkyltrimethylene groups such as —CH(CH₃)CH₂CH₂— and —CH₂CH(CH₃)CH₂—; a tetramethylene group [—CH₂CH₂CH₂CH₂—]; alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂— and —CH₂CH(CH₃)CH₂CH₂—; and a pentamethylene group [—CH₂CH₂CH₂CH₂CH₂—].

As Q′, a divalent linking group containing an ester bond or an ether bond is preferable, and —R⁹¹—O—, —R⁹²—O—C(═O)— or —C(═O)—O—R⁹³—O—C(═O)— is more preferable.

In the group represented by the formula X³-Q″-, the hydrocarbon group for X³ may be either an aromatic hydrocarbon group or an aliphatic hydrocarbon group.

The aromatic hydrocarbon group is a hydrocarbon group having at least one aromatic ring. The aromatic ring is not particularly limited, as long as it is a cyclic conjugated compound having (4 n+2)π electrons (wherein n represents 0 or a natural number), and may be either monocyclic or polycyclic.

The aromatic hydrocarbon ring preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group. Specific examples of aromatic hydrocarbon groups include an aryl group which is an aromatic hydrocarbon ring having one hydrogen atom removed therefrom, such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group or a phenanthryl group; and an alkylaryl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group. The alkyl chain within the arylalkyl group preferably has 1 to 4 carbon atom, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may have a substituent. For example, part of the carbon atoms constituting the aromatic ring within the aromatic hydrocarbon group may be substituted with a hetero atom, or a hydrogen atom bonded to the aromatic ring within the aromatic hydrocarbon group may be substituted with a substituent.

In the former example, a heteroaryl group in which part of the carbon atoms constituting the ring within the aforementioned aryl group has been substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom, and a heteroarylalkyl group in which part of the carbon atoms constituting the aromatic hydrocarbon ring within the aforementioned arylalkyl group has been substituted with the aforementioned heteroatom can be used.

In the latter example, as the substituent for the aromatic hydrocarbon group, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or the like can be used.

The alkyl group as the substituent for the aromatic hydrocarbon group is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent for the aromatic hydrocarbon group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Example of the halogenated alkyl group as the substituent for the aromatic hydrocarbon group includes a group in which part or all of the hydrogen atoms within the aforementioned alkyl group have been substituted with the aforementioned halogen atoms.

The aliphatic hydrocarbon group for X³ may be either a saturated aliphatic hydrocarbon group, or an unsaturated aliphatic hydrocarbon group. Further, the aliphatic hydrocarbon group may be linear, branched or cyclic.

In the aliphatic hydrocarbon group for X³, part of the carbon atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom, or part or all of the hydrogen atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom.

As the “hetero atom” for X³, there is no particular limitation as long as it is an atom other than carbon and hydrogen.

Examples of the halogen atom include a fluorine atom, a chlorine atom, an iodine atom and a bromine atom.

The substituent group containing a hetero atom may consist of a hetero atom, or may be a group containing a group or atom other than a hetero atom.

Specific examples of the substituent group for substituting part of the carbon atoms include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (the H may be replaced with a substituent such as an alkyl group or an acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—. When the aliphatic hydrocarbon group is cyclic, the aliphatic hydrocarbon group may contain any of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of the hydrogen atoms include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group.

The aforementioned alkoxy group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Example of the aforementioned halogenated alkyl group includes a group in which part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms.

As the aliphatic hydrocarbon group, a linear or branched saturated hydrocarbon group, a linear or branched monovalent unsaturated hydrocarbon group, or a cyclic aliphatic hydrocarbon group (aliphatic cyclic group) is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group.

The unsaturated hydrocarbon group preferably has 2 to 10 carbon atoms, more preferably 2 to 5, still more preferably 2 to 4, and most preferably 3. Examples of linear monovalent unsaturated hydrocarbon groups include a vinyl group, a propenyl group (an allyl group) and a butynyl group. Examples of branched monovalent unsaturated hydrocarbon groups include a 1-methylpropenyl group and a 2-methylpropenyl group.

Among the above-mentioned examples, as the unsaturated hydrocarbon group, a propenyl group is particularly desirable.

The aliphatic cyclic group may be either a monocyclic group or a polycyclic group. The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12.

As the aliphatic cyclic group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

When the aliphatic cyclic group does not contain a hetero atom-containing substituent group in the ring structure thereof, the aliphatic cyclic group is preferably a polycyclic group, more preferably a group in which one or more hydrogen atoms have been removed from a polycycloalkane, and a group in which one or more hydrogen atoms have been removed from adamantane is particularly desirable.

When the aliphatic cyclic group contains a hetero atom-containing substituent group in the ring structure thereof, the hetero atom-containing substituent group is preferably —O—, —C(═O)—O—, —S—, —S(═O)₂— or —S(═O)₂—O—. Specific examples of such aliphatic cyclic groups include groups represented by formulas (L1) to (L6) and (S1) to (S4) shown below.

In the formulae, Q″ represents an alkylene group of 1 to 5 carbon atoms, —O—, —S—, —O—R⁹⁴— or —S—R⁹⁵′— (wherein each of R⁹⁴′ and R⁹⁵′ independently represents an alkylene group of 1 to 5 carbon atoms); and m represents 0 or 1.

As the alkylene group for R⁹⁴′ and R⁹⁵′, the same alkylene groups as those described above for R⁹¹ to R⁹⁵ can be used.

In these aliphatic cyclic groups, part of the hydrogen atoms bonded to the carbon atoms constituting the ring structure may be substituted with a substituent. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group and an oxygen atom (═O).

As the alkyl group, an alkyl group of 1 to 5 carbon atoms is preferable, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

As the alkoxy group and the halogen atom, the same groups as the substituent groups for substituting part or all of the hydrogen atoms constituting the aliphatic hydrocarbon group for X³ can be used.

In the present invention, as X³, a cyclic group which may have a substituent is preferable. The cyclic group may be either an aromatic hydrocarbon group which may have a substituent, or an aliphatic cyclic group which may have a substituent, and an aliphatic cyclic group which may have a substituent is preferable.

As the aromatic hydrocarbon group, a naphthyl group which may have a substituent, or a phenyl group which may have a substituent is preferable.

As the aliphatic cyclic group which may have a substituent, an aliphatic polycyclic group which may have a substituent is preferable. As the aliphatic polycyclic group, the aforementioned group in which one or more hydrogen atoms have been removed from a polycycloalkane, and groups represented by the aforementioned formulas (L2) to (L6), (S3) and (S4) are preferable.

Among these examples, as the aforementioned R⁴″, a halogenated alkyl group or a group having X³-Q′- as a substituent is preferable.

When the R⁴″ group has X³-Q′- as a substituent, as R⁴″, a group represented by the formula: X³-Q′-Y³— (in the formula, Q′ and X³ are the same as defined above, and Y³ represents an alkylene group of 1 to 4 carbon atoms which may have a substituent or a fluorinated alkylene group of 1 to 4 carbon atoms which may have a substituent is preferable.

In the group represented by the formula X³-Q′-Y³—, as the alkylene group for Y³, the same alkylene group as those described above for Q′ in which the number of carbon atoms is 1 to 4 can be used.

As the fluorinated alkylene group, the aforementioned alkylene group in which part or all of the hydrogen atoms has been substituted with fluorine atoms can be used.

Specific examples of Y³ include —CF₂—, —CF₂CF₂—, —CF₂CF₂CF₂—, —CF(CF₃)CF₂—, —CF(CF₂CF₃)—, —C(CF₃)₂—, —CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—, —CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—, —C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—, —CF(CF₂CF₂CF₃)—, —C(CF₃)(CF₂CF₃)—; —CHF—, —CH₂CF₂—, —CH₂CH₂CF₂—, —CH₂CF₂CF₂—, —CH(CF₃)CH₂—, —CH(CF₂CF₃)—, —C(CH₃)(CF₃)—, —CH₂CH₂CH₂CF₂—, —CH₂CH₂CF₂CF₂—, —CH(CF₃)CH₂CH₂—, —CH₂CH(CF₃)CH₂—, —CH(CF₃)CH(CF₃)—, —C(CF₃)₂CH₂—; —CH₂—, —CH₂CH₂—, —CH₂CH₂CH₂—, —CH(CH₃)CH₂—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —CH₂CH₂CH₂CH₂—, —CH(CH₃)CH₂CH₂—, —CH₂CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, —CH(CH₂CH₂CH₃)—, and —C(CH₃)(CH₂CH₃)—.

Y³ is preferably a fluorinated alkylene group, and most preferably a fluorinated alkylene group in which the carbon atom bonded to the adjacent sulfur atom is fluorinated. Examples of such fluorinated alkylene groups include —CF₂—, —CF₂CF₂—, —CF₂CF₂CF₂—, —CF(CF₃)CF₂—, —CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—, —CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—, —C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—; —CH₂CF₂—, —CH₂CH₂CF₂—, —CH₂CF₂CF₂—; —CH₂CH₂CH₂CF₂—, —CH₂CH₂CF₂CF₂—, and —CH₂CF₂CF₂CF₂—.

Of these, —CF₂—, —CF₂CF₂—, —CF₂CF₂CF₂— or CH₂CF₂CF₂— is preferable, —CF₂—, —CF₂CF₂— or —CF₂CF₂CF₂— is more preferable, and —CF₂— is particularly desirable.

The alkylene group or fluorinated alkylene group may have a substituent. The alkylene group or fluorinated alkylene group “has a substituent” means that part or all of the hydrogen atoms or fluorine atoms in the alkylene group or fluorinated alkylene group has been substituted with groups other than hydrogen atoms and fluorine atoms.

Examples of substituents which the alkylene group or fluorinated alkylene group may have include an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, and a hydroxyl group.

Specific examples of groups represented by formula R⁴″SO³⁻ in which R⁴″ represents X³-Q′-Y³ include anions represented by the following formulae (1) to (b9).

In the formulae, q1 and q2 each independently represents an integer of 1 to 5; q3 represents an integer of 1 to 12; t3 represents an integer of 1 to 3; r1 and r2 each independently represents an integer of 0 to 3; g represents an integer of 1 to 20; R⁷ represents a substituent; n1 to n6 each independently represents 0 or 1; v0 to v6 each independently represents an integer of 0 to 3; w1 to w6 each independently represents an integer of 0 to 3; and Q″ is the same as defined above.

Examples of the substituent for R⁷ include the aforementioned substituents which may substitute part of the hydrogen atoms bonded to the carbon atoms constituting the ring structure of the aliphatic cyclic group explained above for X³, and the substituents which may substitute a hydrogen atom bonded to the aromatic ring contained in the aforementioned aromatic hydrocarbon group.

If there are two or more of the R⁷ group, as indicated by the values r1, r2, and w1 to w6, then the two or more of the R⁷ groups may be the same or different from each other.

Further, as examples of V⁻ in formula (a6-0-1), an anion represented by general formula (b-3) shown below and an anion represented by general formula (b-4) shown below can be mentioned.

In the formulas, X″ represents an alkylene group of 2 to 6 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom; and each of Y″ and Z″ independently represents an alkyl group of 1 to 10 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom.

In formula (b-3), X″ represents a linear or branched alkylene group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkylene group preferably has 2 to 6 carbon atoms, more preferably 3 to 5 carbon atoms, and most preferably 3 carbon atoms.

In formula (b-4), each of Y″ and Z″ independently represents a linear or branched alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 7 carbon atoms, and most preferably 1 to 3 carbon atoms.

The smaller the number of carbon atoms of the alkylene group for X″ or those of the alkyl group for Y″ and Z″ within the above-mentioned range of the number of carbon atoms, the more the solubility in a resist solvent is improved.

Further, in the alkylene group for X″ or the alkyl group for Y″ and Z″, it is preferable that the number of hydrogen atoms substituted with fluorine atoms is as large as possible because the acid strength increases and the transparency to high energy radiation of 200 nm or less or electron beam is improved.

The amount of fluorine atoms within the alkylene group or alkyl group, i.e., fluorination ratio, is preferably from 70 to 100%, more preferably from 90 to 100%, and it is particularly desirable that the alkylene group or alkyl group be a perfluoroalkylene or perfluoroalkyl group in which all hydrogen atoms are substituted with fluorine atoms.

As V⁻ in formula (a6-0-1), an anion represented by general formula: “R⁴″SO₃ ⁻” (in particular, an anion represented by any one of the aforementioned formulae (b1) to (b9) in which R⁴″ is a group represented by the formula X³-Q′-Y³—) is preferable.

Specific examples of the group represented by formula (a6-0-1) are shown below. In the formulae, V⁻ is the same as defined above.

Structural Unit having a Group Represented by Formula (a6-0-2)

In formula (a6-0-2), Q² represents a single bond or a divalent linking group. The divalent linking group for Q² is the same as defined for the divalent linking group for Q¹ in the aforementioned formula (a6-0-1).

In the present invention, Q² preferably represents a linear or branched alkylene group, an ester bond [—C(═O)—O—], a combination of these, or a single bond.

As the structural unit having a group represented by formula (a6-0-2), a structural unit represented by formula (a6-0-2′) shown below is preferable.

R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; Q², M^(m+)and m are the same as defined above; L¹ represents —O—, —C(═O)—O—, —C(═O)—NH— or a single bond;

R^(y1) represents a single bond or a divalent hydrocarbon group which may have a substituent. The divalent hydrocarbon group which may have a substituent is the same as defined for the aforementioned Q¹, and an alkylene group, a cycloalkylene group, a fluorinated alkylene group, a phenylene group, a naphthylene group or a combination thereof is preferable.

Q² is the same as defined above.

In formula (a6-0-2′), A⁻ represents an organic group containing an anion.

A⁻ is not particularly limited as long as it contains a portion which generates an acid anion upon exposure, and a group which is capable of generating a sulfonate anion, a carbo anion, a carboxylate anion, an imide anion or a sulfonylmethide anion is preferable.

Among these, as A⁻, a group represented by any one of formulae (a0-22-an1) to (a0-22-an4) shown below is preferable.

In the formulae, Z³, Z⁴, Z⁶ and Z⁷ each independently represents —C(═O)— or —SO₂—; Z⁵ represents —C(═O)—, —SO₂— or a single bond; R⁶¹ represents a hydrocarbon group which may have a fluorine atom; and R⁶², R⁶³ and R⁶⁴ each independently represents a hydrocarbon group which may have a fluorine atom.

In formula (a0-22-an2), R⁶¹ represents a hydrocarbon group which may have a fluorine atom. Examples of the hydrocarbon group for R⁶¹ include an alkyl group, a monovalent alicyclic hydrocarbon group, an aryl group and an aralkyl group.

The alkyl group for R⁶¹ preferably has 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, and still more preferably 1 to 4 carbon atoms. The alkyl group may be linear or branched. Specific examples of preferable alkyl groups include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group and an octyl group.

The monovalent alicyclic hydrocarbon group for R⁶¹ preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms. The monovalent alicyclic hydrocarbon group may be polycyclic or monocyclic. As the monocyclic alicyclic hydrocarbon group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane is preferable. The monocycloalkane preferably has 3 to 6 carbon atoms, and specific examples thereof include cyclobutane, cyclopentane and cyclohexane. As the polycyclic alicyclic hydrocarbon group, a group in which one or more hydrogen atoms have been removed from a polycycloalkane is preferable, and the polycyclic group preferably has 7 to 12 carbon atoms. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The aryl group for R⁶¹ preferably has 6 to 18 carbon atoms, and more preferably 6 to 10 carbon atoms. Specifically, a phenyl group is particularly desirable.

As a preferable examples of the aralkyl group for R⁶¹, a group in which an alkylene group of 1 to 8 carbon atoms has been bonded to the aforementioned “aryl group for R⁶¹” can be mentioned. An aralkyl group in which an alkylene group of 1 to 6 carbon atoms has been bonded to the aforementioned “aryl group for R⁶¹” is more preferable, and an aralkyl group in which an alkylene group of 1 to 4 carbon atoms has been bonded to the aforementioned “aryl group for R⁶¹” is most preferable.

The hydrocarbon group for R⁶¹ preferably has part or all of the hydrogen atoms within the hydrocarbon group substituted with fluiorine, and the hydrocarbon group more preferably has 30 to 100% of the hydrogen atoms substituted with fluiorine. Among these, a perfluoroalkyl group in which all of the hydrogen atoms within the alkyl group have been substituted with fluorine atoms is particularly desirable.

The hydrocarbon group for R⁶⁴ which may have a fluorine atom is the same as defined above.

In formula (a0-22-an3), R⁶² and R⁶³ each independently represents a hydrocarbon group which may have a fluorine atom, and is the same as defined for the hydrocarbon group for R⁶¹ which may have a fluorine atom.

As the group represented by formula (a0-2-an1), a group represented by formula (a0-22-an1-1) is preferable.

In the formula, R^(f1) and R^(f2) each independently represents a hydrogen atom, an alkyl group, a fluorine atom or a fluorinated alkyl group, provided that at least one of R^(f1) and R^(f2) represents a fluorine atom or a fluorinated alkyl group; and p0 represents an integer of 1 to 8.

In formula (a6-0-2), M^(m+) represents a countercation, and m represents an integer of 1 to 3.

The countercation for M^(m+) is preferably an organic cation. The organic cation is not particularly limited, and an organic cation conventionally known as the cation moiety of a photo-decomposable base used as a quencher for a resist composition or the cation moiety of an onium salt acid generator for a resist composition can be used. As the organic cation, for example, a cation represented by general formula (m-1) or (m-2) shown below can be preferably used.

In the formulae, to R³″, R⁵″ and R⁶″ each independently represents an aryl group, an alkyl group or an alkenyl group, provided that, in formula (m-1), two of R¹″ to R³″ may be mutually bonded to form a ring with the sulfur atom.

In the formula (m-1), R¹″ to R³″ each independently represents an aryl group, an alkyl group or an alkenyl group. In formula (m-1), two of R¹″ to R³″ may be mutually bonded to form a ring with the sulfur atom.

Further, among R¹″ to R³″, it is preferable that at least one group represent an aryl group.

Among R¹″ to R³″, it is more preferable that two or more groups are aryl groups, and it is particularly desirable that all of to R³″ are aryl groups.

The aryl group, the alkyl group and the alkenyl group for R¹″ to R³″ are the same as defined for the aryl group, the alkyl group and the alkenyl group for R⁴ and R⁵.

Specific examples of preferable cation moieties represented by formula (m-1) include the following.

In formula (I-1-34), R⁰¹ represents an arylene group or an alkylene group; each of R⁰² and R⁰³ independently represents an aryl group or an alkyl group, provided that R⁰² and R⁰³ may be mutually bonded to form a ring with the sulfur atom, and at least one of R⁰¹ to R⁰³ represents an arylene group or an aryl group; W¹ represents a linking group having a valency of n; and n represents 2 or 3.

The arylene group for e is not particularly limited, and examples thereof include arylene groups of 6 to 20 carbon atoms in which part or all of the hydrogen atoms may be substituted. The alkylene group for R⁰¹ is not particularly limited, and examples thereof include linear, branched or cyclic alkylene groups of 1 to 10 carbon atoms.

The aryl group for R⁰² and R⁰³ is not particularly limited, and examples thereof include aryl groups of 6 to 20 carbon atoms in which part or all of the hydrogen atoms may be substituted. The alkyl group for R⁰² and R⁰³ is not particularly limited, and examples thereof include linear, branched or cyclic alkyl groups of 1 to 10 carbon atoms.

Examples of the divalent linking group for W¹ include the same divalent linking groups as those described above for Y¹ and Y² in the aforementioned formula (a0-1). The divalent linking group may be linear, branched or cyclic, but is preferably cyclic. Among these, an arylene group having two carbonyl groups, each bonded to the terminal thereof is preferable.

The trivalent linking group for W¹ is preferably an arylene group combined with three carbonyl groups.

In formula (m-2), R⁵″ and R⁶″ each independently represents an aryl group which may have a substituent or an alkyl group which may have a substituent.

It is preferable that at least one of R⁵″ and R⁶″ is an aryl group, and it is more preferable that both R⁵″ and R⁶″ represent an aryl group.

The aryl group, the alkyl group and the alkenyl group for R⁵″ and R⁶″ are the same as defined for the aryl group, the alkyl group and the alkenyl group for R⁴ and R⁵.

It is particularly desirable that both of R⁵″ and R⁶″ represents a phenyl group.

Specific examples of the cation moiety represented by general formula (m-2) include diphenyliodonium and bis(4-tert-butylphenyl)iodonium.

Examples of other preferable cation moieties include those represented by formulae (I-2) to (I-5) shown below.

In formulae (I-2) to (I-5), u is an integer of 1 to 3, and most preferably 1 or 2.

In formulae (I-2) to (I-4), R^(6a) to R^(8a) each independently represents an alkylene group which may have a substituent or a phenylene group which may have a substituent; and R^(6b) to R^(8b) each independently represents a hydrogen atom, an alkyl group which may have a substituent, a phenyl group which may have a substituent or a naphthyl group which may have a substituent.

In formula (I-5), R⁹ represents an alkyl group which may have a substituent, a phenyl group which may have a substituent, or a naphthyl group which may have a substituent.

As the alkylene group for R^(6a) to R^(8a), a linear or branched alkylene group is preferable. The alkylene group preferably has 1 to 12 carbon atoms, more preferably 1 to 5 carbon atoms, still more preferably 1 to 3 carbon atoms, and most preferably 1 or 2 carbon atoms.

Examples of the substituent for the alkylene group include an alkoxy group, a halogen atom, a hydroxy group, an oxy group (═O), a cyano group, an aryl group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, —C(═O)—O—R⁷″, —O—C(═O)—R⁸″, and —O—R⁹″. The alkoxy group, the halogen atom, the hydroxy group, the oxy group (═O), the cyano group, the aryl group, the alkoxyalkyloxy group, the alkoxycarbonylalkyloxy group, —C(═O)—O—R⁷″, —O—C(═O)—R⁸″ and —O—R⁹″ are the same as defined for the substituent for the substituted aryl group represented by R⁴ and R⁵.

In the formula, the alkyl group for R^(6b) to R^(8b) and R⁹ which may have a substituent is the same as defined for the substituted alkyl group for R⁴ and R⁵ in the aforementioned general formula (m-1).

The substituent for the phenyl group or the naphthyl group for R^(6b) to R^(8b) and R⁹ is the same as defined for the substituent for the substituted aryl group represented by R⁴ and R⁵.

Preferable examples of cations represented by the aforementioned formulae (I-2) to (I-4) are shown below. In the formula, R^(C) represents a substituent described above in the explanation of the aforementioned substituted aryl group (an alkoxy group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, a halogen atom, a hydroxy group, an oxo group (═O), an aryl group, —C(═O)—O—R⁶′, —O—C(═O)—R⁷′, and —O—R⁸′).

Specific examples are shown below.

In formula (m1-3-1), R^(C) represents a substituent. Examples of the substituent include those described above in the explanation of the aforementioned substituted aryl group (an alkyl group, an alkoxy group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, a halogen atom, a hydroxy group, an oxo group (═O), an aryl group, —C(═O)—O—R⁶″, —O—C(═O)—R⁷″, and —O—R⁸″).

Specific examples of structural units represented by formula (a6-0-2″) are shown below. R^(a) represents a hydrogen atom, a methyl group or a tritluoromethyl group, and (M^(m+))_(1/m), is the same as defined above.

In the component (A1), as the structural unit (a6), one type of structural unit may be used alone, or two or more types of structural units may be used in combination.

In the component (A1), the amount of the structural unit (a6) based on the combined total of all structural units constituting the component (A1) is preferably 1 to 50 mol %, more preferably 1 to 45 mol %, still more preferably 3 to 40 mol %, and most preferably 5 to 35 mol %. When the amount of the structural unit (a6) is at least 1 mol %, the effects of improving the lithography properties such as the sensitivity and the resolution can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a6) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

(Structural Unit (a1))

The structural unit (a1) is a structural unit which does not fall under the definition of the structural units (a0) and (a6), and contains an acid decomposable group that exhibits increased polarity by the action of acid.

The term “acid decomposable group” refers to a group in which at least a part of the bond within the structure thereof is cleaved by the action of acid generated upon exposure (acid generated from the structural unit (a6-0-1) or (a6-0-2), acid generated from the component (B) described later, and the like).

Examples of acid decomposable groups which exhibit increased polarity by the action of an acid include groups which are decomposed by the action of an acid to form a polar group.

Examples of the polar group include a carboxy group, a hydroxy group, an amino group and a sulfo group (—SO₃H). Among these, a polar group containing —OH in the structure thereof (hereafter, referred to as “OH-containing polar group”) is preferable, a carboxy group or a hydroxy group is more preferable, and a carboxy group is particularly desirable.

More specifically, as an example of an acid decomposable group, a group in which the aforementioned polar group has been protected with an acid dissociable group (such as a group in which the hydrogen atom of the OH-containing polar group has been protected with an acid dissociable group) can be given.

An “acid dissociable group” is a group in which at least the bond between the acid dissociable group and the adjacent carbon atom is cleaved by the action of acid generated upon exposure. It is necessary that the acid dissociable group that constitutes the acid decomposable group is a group which exhibits a lower polarity than the polar group generated by the dissociation of the acid dissociable group. Thus, when the acid dissociable group is dissociated by the action of acid, a polar group exhibiting a higher polarity than that of the acid dissociable group is generated, thereby increasing the polarity. As a result, the polarity of the entire component (A1) is increased. By the increase in the polarity, the solubility in an alkali developing solution changes and, the solubility in an alkali developing solution is relatively increased, whereas the solubility in a developing solution containing an organic solvent (organic solvent) is relatively decreased.

The acid dissociable group is not particularly limited, and any of the groups that have been conventionally proposed as acid dissociable groups for the base resins of chemically amplified resists can be used. Generally, groups that form either a cyclic or chain-like tertiary alkyl ester with the carboxyl group of the (meth)acrylic acid, and acetal-type acid dissociable groups such as alkoxyalkyl groups are widely known.

Here, a tertiary alkyl ester describes a structure in which an ester is formed by substituting the hydrogen atom of a carboxyl group with a chain-like or cyclic tertiary alkyl group, and a tertiary carbon atom within the chain-like or cyclic tertiary alkyl group is bonded to the oxygen atom at the terminal of the carbonyloxy group (—C(═O)—O—). In this tertiary alkyl ester, the action of acid causes cleavage of the bond between the oxygen atom and the tertiary carbon atom, thereby forming a carboxy group.

The chain-like or cyclic alkyl group may have a substituent.

Hereafter, for the sake of simplicity, groups that exhibit acid dissociability as a result of the formation of a tertiary alkyl ester with a carboxyl group are referred to as “tertiary alkyl ester-type acid dissociable groups”.

Examples of tertiary alkyl ester-type acid dissociable groups include aliphatic branched, acid dissociable groups and aliphatic cyclic group-containing acid dissociable groups.

The term “aliphatic branched” refers to a branched structure having no aromaticity. The “aliphatic branched, acid dissociable group” is not limited to be constituted of only carbon atoms and hydrogen atoms (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated.

As an example of the aliphatic branched, acid dissociable group, for example, a group represented by the formula —C(R⁷¹)(R⁷²)(R⁷³) can be given. (in the formula, each of R⁷¹ to R⁷³ independently represents a linear alkyl group of 1 to 5 carbon atoms). The group represented by the formula —C(R⁷¹)(R⁷²)(R⁷³) preferably has 4 to 8 carbon atoms, and specific examples include a tert-butyl group, a 2-methyl-2-butyl group, a 2-methyl-2-pentyl group and a 3-methyl-3-pentyl group.

Among these, a tert-butyl group is particularly desirable.

The term “aliphatic cyclic group” refers to a monocyclic group or polycyclic group that has no aromaticity.

In the “aliphatic cyclic group-containing acid dissociable group”, the “aliphatic cyclic group” may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituents is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated.

The aliphatic cyclic group may be either a monocyclic group or a polycyclic group.

The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. As such aliphatic cyclic groups, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane which may or may not be substituted with a lower alkyl group, a fluorine atom or a fluorinated alkyl group, may be used. Specific examples of aliphatic cyclic hydrocarbon groups include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. In these aliphatic cyclic hydrocarbon groups, part of the carbon atoms constituting the ring may be replaced with an ethereal oxygen atom (—O—).

Examples of aliphatic cyclic group-containing acid dissociable groups include

(i) a monovalent aliphatic cyclic group in which a substituent (a group or an atom other than hydrogen) is bonded to the carbon atom on the ring skeleton to which an atom adjacent to the acid dissociable group (e.g., “—O—” within “—C(═O)—O— group”) is bonded to form a tertiary carbon atom (hereafter, this group is sometimes referred to as a “group having a tertiary carbon atom ont the ring skeleton of a cyclic alkyl group”); and

(ii) a group which has a branched alkylene group containing a tertiary carbon atom, and a monovalent aliphatic cyclic group to which the tertiary carbon atom is bonded.

In the group (i), as the substituent bonded to the carbon atom to which an atom adjacent to the acid dissociable group on the ring skeleton of the aliphatic cyclic group, an alkyl group which may have a substituent can be mentioned. Examples of the alkyl group include the same groups as those represented by R¹⁴ in formulas (1-1) to (1-9) described later.

Specific examples of the group (i) include groups represented by general formulas (1-1) to (1-9) shown below.

Specific examples of the group (ii) include groups represented by general formulas (2-1) to (2-6) shown below.

In the formulas above, R¹⁴ represents an alkyl group which may have a substituent; and g represents an integer of 0 to 8.

In the formulas above, each of R¹⁵ and R¹⁶ independently represents an alkyl group.

In formulas (1-1) to (1-9), the alkyl group for R¹⁴ may be linear, branched or cyclic, and is preferably linear or branched.

The linear alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 4, and still more preferably 1 or 2. Specific examples include a methyl group, an ethyl group, an n-propyl group, an n-butyl group and an n-pentyl group. Among these, a methyl group, an ethyl group or an n-butyl group is preferable, and a methyl group or an ethyl group is more preferable.

The branched alkyl group preferably has 3 to 10 carbon atoms, and more preferably 3 to 5. Specific examples of such branched alkyl groups include an isopropyl group, an isobutyl group, a tert-butyl group, an isopentyl group and a neopentyl group, and an isopropyl group is particularly desirable.

The linear or branched alkyl group may have a substituent. Examples of the substituent include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O), a cyano group and a carboxy group.

The cyclic alkyl group preferably has 3 to 10 carbon atoms, and more preferably 5 to 8. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane. Examples of the monocycloalkane include cyclopentane and cyclohexane.

Examples of polycycloalkanes include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The cyclic alkyl group may have a substituent. Specifically, part or all of the hydrogen atoms constituting the alkyl group may be substituted with an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), a cyano group, a carboxy group or the like, and part or all of the carbon atoms constituting the alkyl group may be substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom.

g is preferably an integer of 0 to 3, more preferably 1 to 3, and still more preferably 1 or 2.

In formulas (2-1) to (2-6), as the alkyl group for R¹⁵ and R¹⁶, the same alkyl groups as those for R¹⁴ can be used.

In formulas (1-1) to (1-9) and (2-1) to (2-6), part of the carbon atoms constituting the ring may be replaced with an ethereal oxygen atom (—O—).

Further, in formulas (1-1) to (1-9) and (2-1) to (2-6), one or more of the hydrogen atoms bonded to the carbon atoms constituting the ring may be substituted with a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom and a fluorinated alkyl group.

An “acetal-type acid dissociable group” generally substitutes a hydrogen atom at the terminal of an OH-containing polar group such as a carboxy group or hydroxyl group, so as to be bonded with an oxygen atom. When acid is generated upon exposure, the generated acid acts to break the bond between the acetal-type acid dissociable group and the oxygen atom to which the acetal-type, acid dissociable group is bonded, thereby forming an OH-containing polar group such as a carboxy group or a hydroxy group.

Examples of acetal-type acid dissociable groups include groups represented by general formula (p1) shown below.

In the formula, R¹′ and R²′ each independently represent a hydrogen atom or an alkyl group of 1 to 5 carbon atoms; n represents an integer of 0 to 3; and Y represents an alkyl group of 1 to 5 carbon atoms or an aliphatic cyclic group.

In general formula (p1), n is preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 0.

In formula (p1), R¹′ and R²′ each independently represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms. The alkyl group of 1 to 5 carbon atoms for R¹′ and R²′ is the same as defined for the alkyl group of 1 to 5 carbon atoms for R, preferably a methyl group or an ethyl group, and most preferably a methyl group.

The alkyl group of 1 to 5 carbon atoms for Y is the same as defined for the alkyl group of 1 to 5 carbon atoms for R¹′ and R²′.

The cyclic alkyl group for Y preferably has 4 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane which may or may not be substituted with a fluorine atom or a fluorinated alkyl group may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane.

Further, and Y may each independently represent an alkyl group of 1 to 5 carbon atoms, and the terminal of R¹′ may be bonded to the terminal of Y.

In such a case, the cyclic group formed by the bonding is preferably a 4- to 7-membered ring, and more preferably a 4- to 6-membered ring. Specific examples of the cyclic group include tetrahydropyranyl group and tetrahydrofuranyl group.

In the present invention, examples of the structural unit (a1)) include a structural unit (a11) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid; a structural unit (a12) derived from hydroxystyrene or a hydroxystyrene derivative in which at least a part of the hydrogen atom of the hydroxy group is protected with a substituent containing an acid decomposable group; and a structural unit (a13) derived from vinylbenzoic acid or a vinylbenzoic acid derivative in which at least a part of the hydrogen atom within —C(═O)—OH is protected with a substituent containing an acid decomposable group.

In the present descriptions and claims, the term “structural unit derived from an acrylate ester” refers to a structural unit which is formed by the cleavage of the ethylenic double bond of an acrylate ester.

An “acrylate ester” refers to a compound in which the terminal hydrogen atom of the carboxy group of acrylic acid (CH₂═CH—COOH) has been substituted with an organic group.

The acrylate ester may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent. The substituent that substitutes the hydrogen atom bonded to the carbon atom on the α-position is atom other than hydrogen or a group, and examples thereof include an alkyl group of 1 to 5 carbon atoms, a halogenated alkyl group of 1 to 5 carbon atoms and a hydroxyalkyl group of 1 to 5 carbon atoms. A carbon atom on the α-position of an acrylate ester refers to the carbon atom bonded to the carbonyl group, unless specified otherwise.

Hereafter, an acrylate ester having the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent is sometimes referred to as “α-substituted acrylate ester”. Further, acrylate esters and α-substituted acrylate esters are collectively referred to as “(α-substituted) acrylate ester”.

In the α-substituted acrylate ester, the alkyl group as the substituent on the α-position is preferably a linear or branched alkyl group, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group and a neopentyl group.

Specific examples of the halogenated alkyl group of 1 to 5 carbon atoms as the substituent on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group of 1 to 5 carbon atoms as the substituent on the α-position” are substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

Specific examples of the hydroxyalkyl group of 1 to 5 carbon atoms as the substituent on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group of 1 to 5 carbon atoms as the substituent on the α-position” are substituted with a hydroxy group.

It is preferable that a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms is bonded to the α-position of the α-substituted acrylate ester, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is more preferable, and in terms of industrial availability, a hydrogen atom or a methyl group is the most desirable.

A “structural unit derived from hydroxystyrene or a hydroxystyrene derivative” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of hydroxystyrene or a hydroxystyrene derivative.

The term “hydroxystyrene derivative” includes compounds in which the hydrogen atom at the α-position of hydroxystyrene has been substituted with another substituent such as an alkyl group or a halogenated alkyl group; and derivatives thereof. Here, the α-position (carbon atom on the α-position) refers to the carbon atom having the benzene ring bonded thereto, unless specified otherwise.

A “structural unit derived from vinylbenzoic acid or a vinylbenzoic acid derivative” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of vinylbenzoic acid or a vinylbenzoic acid derivative.

The term “vinylbenzoic acid derivative” includes compounds in which the hydrogen atom at the α-position of vinylbenzoic acid has been substituted with another substituent such as an alkyl group or a halogenated alkyl group; and derivatives thereof. Here, the α-position (carbon atom on the α-position) refers to the carbon atom having the benzene ring bonded thereto, unless specified otherwise.

Herebelow, the structural unit (a11), the structural unit (a12) and the structural unit (a13) will be described.

(Structural Unit (a11))

More specific examples of the structural unit (a11) include a structural unit represented by general formula (a11-0-1) shown below and a structural unit represented by general formula (a11-0-2) shown below.

In the formulae, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X¹ represents an acid dissociable group; Y³″ represents a divalent linking group; and X² represents an acid dissociable group.

In general formula (a11-0-1), R is the same as defined for R¹ in the aforementioned formula (a0-1).

X¹ is not particularly limited as long as it is an acid dissociable group. Examples thereof include the aforementioned tertiary alkyl ester-type acid dissociable groups and acetal-type acid dissociable groups, and tertiary alkyl ester-type acid dissociable groups are preferable.

In general formula (a11-0-2), R is the same as defined above.

X² is the same as defined for X¹ in general formula (a11-0-1).

The divalent linking group for Y³″ is not particularly limited, and preferable examples thereof include a divalent hydrocarbon group which may have a substituent and a divalent linking group containing a hetero atom, which were explained above as examples of the divalent linking group for Y¹ and Y² in the aforementioned formula (a0-1).

Among these, as the divalent linking group for Y³″, a linear or branched alkylene group, a divalent alicyclic hydrocarbon group or a divalent linking group containing a hetero atom is particularly desirable. Among these, an alkylene group or a divalent linking group containing a hetero atom is more preferable.

Specific examples of the structural unit (a11) include structural units represented by general formulas (a1-1) to (a1-4) shown below.

In the formulas, R, R¹′, R²′, n, Y and Y³″ are the same as defined above; and X′ represents a tertiary alkyl ester-type acid dissociable group.

In the formulas, the tertiary alkyl ester-type acid dissociable group for X′ include the same tertiary alkyl ester-type acid dissociable groups as those described above.

As R¹′, R²′, n and Y are respectively the same as defined for R¹′, R²′, n and Y in general formula (p1) described above in connection with the “acetal-type acid dissociable group”.

As examples of Y³″, the same groups as those described above for Y³″ in general formula (a11-0-2) can be given.

Specific examples of structural units represented by general formula (a1-1) to (a1-4) are shown below.

In the formulae shown below, R^(a) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

In the present invention, it is particularly desirable that the structural unit (a11) include at least one member selected from the group consisting of structural units represented by general formulae (a11-0-11) to (a11-0-15) shown below and a structural unit represented by general formula (a11-0-2) shown below.

Among these examples, as the structural unit (a1), it is preferable to include at least one structural unit selected from the group consisting of structural units represented by general formulae (a11-0-11) to (a11-0-15) shown below, and it is more preferable to include at least one structural unit selected from the group consisting of structural units represented by general formulae (a11-0-11) to (a11-0-13) and (a11-0-15).

In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²¹ represents an alkyl group; R²² represents a group which forms an aliphatic monocyclic group with the carbon atom to which R²² is bonded; R²³ represents a branched alkyl group; R²⁴ represents a group which forms an aliphatic polycyclic group with the carbon atom to which R²⁴ is bonded; R²⁵ represents a linear alkyl group of 1 to 5 carbon atoms; R¹⁵ and R¹⁶ each independently represents an alkyl group; Y³″ represents a divalent linking group; and X² an acid dissociable group.

In the formulae, R, Y³″ and X² are the same as defined above.

In general formula (a11-0-11), as the alkyl group for R²¹, the same alkyl groups as those described above for R¹⁴ in formulae (1-1) to (1-9) can be used, preferably a methyl group, an ethyl group, an isopropyl group or a cyclic alkyl group (preferably a polycyclic group).

As the aliphatic monocyclic group formed by R²² and the carbon atoms to which R²² is bonded, the same aliphatic cyclic groups as those described above for the aforementioned tertiary alkyl ester-type acid dissociable group and which are monocyclic can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane. The monocycloalkane is preferably a 3- to 11-membered ring, more preferably a 3- to 8-membered ring, still more preferably a 4- to 6-membered ring, and most preferably a 5- or 6-membered ring.

The monocycloalkane may or may not have part of the carbon atoms constituting the ring replaced with an ether bond (—O—).

Further, the monocycloalkane may have a substituent such as an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group of 1 to 5 carbon atoms.

As an examples of R²² constituting such an aliphatic cyclic group, an alkylene group which may have an ether bond (—O—) interposed between the carbon atoms can be given.

Specific examples of structural units represented by general formula (a11-0-11) include structural units represented by the aforementioned formulas (a1-1-16) to (a1-1-23), (a1-1-27), (a1-1-31) and (a1-1-37). Among these, a structural unit represented by general formula (a11-1-02) shown below which includes the structural units represented by the aforementioned formulas (a1-1-16), (a1-1-17), (a1-1-20) to (a1-1-23), (a1-1-27), (a1-1-31), (a1-1-32), (a1-1-33) and (a1-1-37) is preferable. Further, a structural unit represented by general formula (a11-1-02′) shown below is also preferable.

In the formulae, h represents an integer of 1 to 4, and preferably 1 or 2.

In the formulae, R and R²¹ are the same as defined above; and h represents an integer of 1 to 4.

In general formula (a11-0-12), as the branched alkyl group for R²³, the same alkyl groups as those described above for R¹⁴ which are branched can be used, and an isopropyl group is particularly desirable.

As the aliphatic polycyclic group formed by R²⁴ and the carbon atoms to which R²⁴ is bonded, the same aliphatic cyclic groups as those described above for the aforementioned tertiary alkyl ester-type acid dissociable group and which are polycyclic can be used.

Specific examples of structural units represented by general formula (a11-0-12) include structural units represented by the aforementioned formulas (a1-1-26) and (a1-1-28) to (a1-1-30).

As the structural unit (a11-0-12), a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a 2-adamantyl group is preferable, and a structural unit represented by the aforementioned formula (a1-1-26) is particularly desirable.

In general formula (a11-0-13), R and R²⁴ are the same as defined above.

As the linear alkyl group for R²⁵, the same linear alkyl groups as those described above for R¹⁴ in the aforementioned formulas (1-1) to (1-9) can be mentioned, and a methyl group or an ethyl group is particularly desirable.

Specific examples of structural units represented by general formula (a11-0-13) include structural units represented by the aforementioned formulas (a1-1-1), (a1-1-2) and (a1-1-7) to (a1-1-15) which were described above as specific examples of the structural unit represented by general formula (a1-1).

As the structural unit (a11-0-13), a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a 2-adamantyl group is preferable, and a structural unit represented by the aforementioned formula (a1-1-1) or (a1-1-2) is particularly desirable.

Further, a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a “group in which one or more hydrogen atoms have been removed from tetracyclododecane” is also preferable, and a structural unit represented by the aforementioned formula (a1-1-8), (a1-1-9) or (a1-1-30) is also preferable.

In general formula (a11-0-14), R and R²² are the same as defined above. R¹⁵ and R¹⁶ are the same as R¹⁵ and R¹⁶ in the aforementioned general formulae (2-1) to (2-6), respectively.

Specific examples of structural units represented by general formula (a11-0-14) include structural units represented by the aforementioned formulae (a1-1-35) and (a1-1-36) which were described above as specific examples of the structural unit represented by general formula (a1-1).

In general formula (a11-0-15), R and R²⁴ are the same as defined above. R¹⁵ and R¹⁶ are the same as R¹⁵ and R¹⁶ in the aforementioned general formulae (2-1) to (2-6), respectively.

Specific examples of structural units represented by general formula (a11-0-15) include structural units represented by the aforementioned formulae (a1-1-4) to (a1-1-6) and (a1-1-34) which were described above as specific examples of the structural unit represented by general formula (a1-1).

Examples of structural units represented by general formula (a11-0-2) include structural units represented by the aforementioned formulae (a1-3) and (a1-4), and a structural unit represented by formula (a1-3) is particularly desirable.

Examples of structural units represented by general formula (a11-0-2) include structural units represented by the aforementioned formulas (a1-1-26) and (a1-1-28) to (a1-1-30). Preferable examples of such structural units include a structural unit represented by general formula (a1-3-01) shown below, a structural unit represented by general formula (a1-3-02) shown below, and a structural unit represented by general formula (a1-3-03) shown below.

In the formulae, R is the same as defined above; R¹³ represents a hydrogen atom or a methyl group; R¹⁴ represents an alkyl group; e represents an integer of 1 to 10; and n′ represents an integer of 0 to 3.

In the formula, R is as defined above; each of Y²′ and Y²″ independently represents a divalent linking group; X′ represents an acid dissociable group; and w represents an integer of 0 to 3.

In general formulas (a1-3-01) and (a1-3-02), R¹³ is preferably a hydrogen atom.

R¹⁴ is the same as defined for R in the aforementioned formulas (1-1) to (1-9).

e is preferably an integer of 1 to 8, more preferably an integer of 1 to 5, and most preferably 1 or 2.

n′ is preferably 1 or 2, and most preferably 2.

Specific examples of structural units represented by general formula (a1-3-01) include structural units represented by the aforementioned formulas (a1-3-25) and (a1-3-26).

Specific examples of structural units represented by general formula (a1-3-02) include structural units represented by the aforementioned formulas (a1-3-27) and (a1-3-28).

In general formula (a1-3-03), as the divalent linking group for Y²′ and Y²″, the same groups as those described above for Y² in general formula (a1-3) can be used.

As Y²′, a divalent hydrocarbon group which may have a substituent is preferable, a linear aliphatic hydrocarbon group is more preferable, and a linear alkylene group is still more preferable. Among linear alkylene groups, a linear alkylene group of 1 to 5 carbon atoms is preferable, and a methylene group or an ethylene group is particularly desirable.

As Y²″, a divalent hydrocarbon group which may have a substituent is preferable, a linear aliphatic hydrocarbon group is more preferable, and a linear alkylene group is still more preferable. Among linear alkylene groups, a linear alkylene group of 1 to 5 carbon atoms is preferable, and a methylene group or an ethylene group is particularly desirable.

As the acid dissociable group for X′, the same groups as those described above can be used. X′ is preferably a tertiary alkyl ester-type acid dissociable group, more preferably the aforementioned group (i) in which a substituent is bonded to the carbon atom to which an atom adjacent to the acid dissociable group is bonded to on the ring skeleton to form a tertiary carbon atom. Among these, a group represented by the aforementioned general formula (1-1) is particularly desirable.

w represents an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 1.

As the structural unit represented by general formula (a1-3-03), a structural unit represented by general formula (a1-3-03-1) or (a1-3-03-2) shown below is preferable, and a structural unit represented by general formula (a1-3-03-1) is particularly desirable.

In the formulas, R and R¹⁴ are the same as defined above; a′ represents an integer of 1 to 10; b′ represents an integer of 1 to 10; and t represents an integer of 0 to 3.

In general formulas (a1-3-03-1) and (a1-3-03-2), a′ is the same as defined above, preferably an integer of 1 to 8, more preferably 1 to 5, and most preferably 1 or 2.

b′ is the same as defined above, preferably an integer of 1 to 8, more preferably 1 to 5, and most preferably 1 or 2.

t is preferably an integer of 1 to 3, and most preferably 1 or 2.

Specific examples of structural units represented by general formula (a1-3-03-1) or (a1-3-03-2) include structural units represented by the aforementioned formulas (a1-3-29) to (a1-3-32).

(Structural Unit (a12), Structural Unit (a13))

In the present specification, the structural unit (a12) is a structural unit derived from hydroxystyrene or a derivative thereof in which at least a part of the hydrogen atom within the hydroxy group is protected with a substituent containing an acid decomposable group.

Further, the structural unit (a13) is a structural unit derived from vinylbenzoic acid or a derivative thereof in which at least a part of the hydrogen atom within —C(═O)—OH is protected with a substituent containing an acid decomposable group.

In the structural unit (a12) and the structural unit (a13), as the substituent containing an acid decomposable group, the tertiary alkyl ester-type acid dissociable group and the acetal-type acid dissociable group described above for the structural unit (a11) can be given as preferable examples.

Preferable examples of the structural unit (a12) and the structural unit (a13) include structural units represented by general formulae (a12-1) to (a12-4) and (a13-1) shown below.

In formulae (a12-1) to (a12-4) and (a13-1), R is the same as defined above; R⁸⁸ represents a halogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; q represents an integer of 0 to 4; R¹′ is the same as defined above; n represents an integer of 0 to 3; W represents an aliphatic cyclic group, an aromatic hydrocarbon group or an alkyl group of 1 to 5 carbon atoms; r represents an integer of 1 to 3; R ⁴¹, R⁴² and R⁴³ each independently represents a linear or branched alkyl group; and X¹ represents an acid dissociable group.

In the formulae (a12-1) to (a12-4) and (a13-1), the bonding position of “—O—CHR¹′—O—(CH₂)_(n)—W”, “—O—C(O)—O—C(R⁴¹)(R⁴²)(R⁴³)”, “—O—C(O)—O—X¹”, “—O—(CH₂)_(r)—C(O)—O—X¹” and “—C(O)—O—X¹” on the phenyl group may be the o-position, the m-position or the p-position. In terms of the effects of the present invention, the p-position is most preferable.

R⁸⁸ represents a halogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

Examples of the halogen atom for R⁸⁸ include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

The alkyl group of 1 to 5 carbon atoms and the halogenated alkyl group of 1 to 5 carbon atoms for R⁸⁸ are the same as defined for the alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms for R, respectively.

When q is 1, the bonding position of R⁸⁸ may be any of the o-position, the m-position and the p-position.

When q is 2, a desired combination of the bonding positions can be used.

However, 1≦p+q≦5.

q represents an integer of 0 to 4, preferably 0 or 1, and most preferably 0 from an industrial viewpoint.

n is an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 1.

<f0> The aliphatic cyclic group for W is a monovalent aliphatic cyclic group. The aliphatic cyclic group can be selected appropriately, for example, from the multitude of groups that have been proposed for conventional ArF resists. Specific examples of the aliphatic cyclic group include an aliphatic monocyclic group of 5 to 7 carbon atoms and an aliphatic polycyclic group of 10 to 16 carbon atoms.

The aliphatic cyclic group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituents is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon groups), and may have an oxygen atom or the like in the ring structure thereof

As the aliphatic monocyclic group of 5 to 7 carbon atoms, a group in which one hydrogen atom has been removed from a monocycloalkane can be mentioned, and specific examples include a group in which one hydrogen atom has been removed from cyclopentane or cyclohexane.

Examples of the aliphatic polycyclic group of 10 to 16 carbon atoms include groups in which one hydrogen atom has been removed from a bicycloalkane, tricycloalkane, tetracycloalkane or the like. Specific examples include groups in which one hydrogen atom has been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Of these, an adamantyl group, a norbornyl group and a tetracyclododecyl group is preferred industrially, and an adamantyl group is particularly desirable.

As the aromatic cyclic hydrocarbon group for W, aromatic polycyclic groups of 10 to 16 carbon atoms can be mentioned. Examples of such aromatic polycyclic groups include groups in which one hydrogen atom has been removed from naphthalene, anthracene, phenanthrene or pyrene. Specific examples include a 1-naphthyl group, a 2-naphthyl group, a 1-anthryl group, a 2-anthryl group, a 1-phenanthryl group, a 2-phenanthryl group, a 3-phenanthryl group and a 1-pyrenyl group, and a 2-naphthyl group is preferred industrially.

The alkyl group of 1 to 5 carbon atoms for W is the same as defined for the alkyl group of 1 to 5 carbon atoms which may be bonded to the α-position of hydroxystyrene, preferably a methyl group or an ethyl group, and most preferably an ethyl group.

Each of R⁴¹ to R⁴³ is preferably an alkyl group of 1 to 5 carbon atoms, and more preferably an alkyl group of 1 to 3 carbon atoms. Specific examples thereof are the same as defined for the alkyl group of 1 to 5 carbon atoms for R.

The acid dissociable group for X¹ is the same as defined for the acid dissociable group for X¹ in the aforementioned formula (a11-0-1).

r is preferably 1 or 2, and more preferably 1.

Among the structural unit (a12) and the structural unit (a13), the structural unit (a12) is preferable, and a structural unit represented by general formula (a12-1) or a structural unit represented by general formula (a12-4) is more preferable.

Specific examples of preferable structural units (a12) are shown below.

As the structural unit (a12), at least one member selected from chemical formulae (a12-1-1) to (a12-1-12) is preferable, and any one of chemical formula (a12-1-l), (a12-1-2) and (a12-1-5) to (a12-1-12) is most preferable.

As the structural unit (a1) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

As the structural unit (a1), a structural unit (a11) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent is preferable.

In the component (A1), the amount of the structural unit (a1) based on the combined total of all structural units constituting the component (A1) is preferably 10 to 70 mol %, more preferably 15 to 66 mol %, still more preferably 20 to 60 mol %, and most preferably 35 to 50 mol %.

When the amount of the structural unit (a1) is at least as large as the lower limit of the above-mentioned range, a pattern can be easily formed using a resist composition prepared from the component (A1), and various lithography properties such as sensitivity, resolution, LWR and the like are improved. On the other hand, when the amount of the structural unit (a1) is no more than the upper limit of the above-mentioned range, a good balance can be reliably achieved with the other structural units.

(Other Structural Units)

The component (A1) may also have a structural unit other than the above-mentioned structural units (a0), (a6) and (a1), as long as the effects of the present invention are not impaired.

As such a structural unit, any other structural unit which cannot be classified as the aforementioned structural units can be used without any particular limitation, and any of the multitude of conventional structural units used within resist resins for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

Examples of the other structural unit include a structural unit (a2) containing a lactone-containing cyclic group, a structural unit (a3) containing a polar group (provided that structural units which fall under the definition of the structural units (a0), (a6) or (a1) are excluded), and a structural unit (a4) containing an acid non-dissociable aliphatic polycyclic group.

Structural Unit (a2)

The component (A1) preferably includes a structural unit (a2) containing a lactone-containing cyclic group, as well as the structural units (a0), (a6) and (a1).

When the component (A1) is used for forming a resist film, the structural unit (a2) containing a lactone-containing cyclic group is effective in improving the adhesion between the resist film and the substrate. Further, in an alkali developing process, the structural unit (a2) is effective in terms of improving the affinity for a water-containing developing solution such as an alkali developing solution.

The aforementioned structural unit (a0), (a6) or (a1) which contains a lactone-containing cyclic group falls under the definition of the structural unit (a2); however, such a structural unit is regarded as a structural unit (a0), (a6) or (a1), and does not fall under the definition of the structural unit (a2).

The term “lactone ring-containing group” refers to a cyclic group including a ring containing a —O—C(═O)— structure (lactone ring). The term “lactone ring” refers to a single ring containing a —O—C(O)— structure, and this ring is counted as the first ring. A lactone-containing cyclic group in which the only ring structure is the lactone ring is referred to as a monocyclic group, and groups containing other ring structures are described as polycyclic groups regardless of the structure of the other rings. The lactone-containing cyclic group may be either a monocyclic group or a polycyclic group.

The lactone-containing cyclic group for the structural unit (a2) is not particularly limited, and an arbitrary structural unit may be used. Specific examples of lactone-containing monocyclic groups include a group in which one hydrogen atom has been removed from a 4- to 6-membered lactone ring, such as a group in which one hydrogen atom has been removed from β-propionolatone, a group in which one hydrogen atom has been removed from γ-butyrolactone, and a group in which one hydrogen atom has been removed from δ-valerolactone. Further, specific examples of lactone-containing polycyclic groups include groups in which one hydrogen atom has been removed from a lactone ring-containing bicycloalkane, tricycloalkane or tetracycloalkane.

Specific examples include groups represented by general formulae (a2-2-1) to (a2-2-7) shown below.

In the formulas, R¹ independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, —COOR″, OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group; s″ represents an integer of 0 to 2; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and m represents 0 or 1.

The alkyl group for R¹ is preferably an alkyl group of 1 to 6 carbon atoms. Further, the alkyl group is preferably a linear alkyl group or a branched alkyl group. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group and a hexyl group. Among these, a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

As the alkoxy group, an alkoxy group of 1 to 6 carbon atoms is preferable.

Further, the alkoxy group is preferably a linear or branched alkoxy group. Specific examples of the alkoxy group include the aforementioned alkyl groups for the substituent having an oxygen atom (—O—) bonded thereto.

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

As examples of the halogenated alkyl group, groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups for the substituent have been substituted with the aforementioned halogen atoms can be given. As the halogenated alkyl group, a fluorinated alkyl group is preferable, and a perfluoroalkyl group is particularly desirable.

In the —COOR″ group and the —OC(═O)R″ group, R″ represents a hydrogen atom or a linear, branched or cyclic alkyl group of 1 to 15 carbon atoms.

When R″ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1 to 5 carbon atoms, and most preferably a methyl group or an ethyl group.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The hydroxyalkyl group preferably has 1 to 6 carbon atoms, and specific examples thereof include the aforementioned alkyl groups for the substituent in which at least one hydrogen atom has been substituted with a hydroxy group.

A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom, preferably an alkylene group of 1 to 5 carbon atoms, an oxygen atom (—O—) or a sulfur atom (—S—), and more preferably an alkylene group of 1 to 5 carbon atoms or —O—. The alkylene group of 1 to 5 carbon atoms is preferably a methylene group or a dimethylmethylene group, and most preferably a methylene group. As the alkylene group of 1 to 5 carbon atoms, a methylene group or a dimethylethylene group is preferable, and a methylene group is particularly desirable.

Specific examples of groups represented by general formulae (a2-2-1) to (a2-2-7) are shown below.

More specifically, examples of the structural unit (a2) include structural units represented by general formula (a2-0) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²⁸ represents a lactone ring-containing group; and R²⁹ represents a single bond or a divalent linking group.

In general formula (a2-0), R is the same as defined above.

R²⁸ is the same as defined for the aforementioned lactone-ring containing group.

R²⁹ may be either a single bond or a divalent linking group. In terms of the effects of the present invention, a divalent linking group is preferable.

The divalent linking group for R²⁹ is not particularly limited, and examples thereof include the same divalent linking groups as those described above for Y¹ or Y² in the aforementioned formula (a0-1). Among these, an alkylene group or a divalent linking group containing an ester bond (—C(═O)—O—) is preferable.

As the alkylene group, a linear or branched alkylene group is preferable. Specific examples include the same linear alkylene groups and branched alkylene groups as those described above for the aliphatic hydrocarbon group represented by Y².

As the divalent linking group containing an ester bond, a group represented by general formula: —R³⁰—C(═O)—O— (in the formula, R³⁰ represents a divalent linking group) is particularly desirable. That is, the structural unit (a2^(s)) is preferably a structural unit represented by general formula (a2-0-1) shown below.

In the formula, R and R²⁸ are the same as defined above; and R³⁰ represents a divalent linking group.

R³⁰ is not particularly limited, and examples thereof include the same divalent linking groups as those described above for Y¹ and Y² in the aforementioned formula (a0-1).

As the divalent linking group for R³⁰, a linear or branched alkylene group, an aliphatic hydrocarbon group having a ring in the structure thereof, or a divalent linking group containing a hetero atom is preferable, and a linear or branched alkylene group or a divalent linking group containing a hetero atom is more preferable.

As the linear alkylene group, a methylene group or an ethylene group is preferable, and a methylene group is particularly desirable.

As the branched alkylene group, an alkylmethylene group or an alkylethylene group is preferable, and —CH(CH₃)—, —C(CH₃)₂— or —C(CH₃)₂CH₂— is particularly desirable.

As the divalent linking group containing an oxygen atom, a divalent linking group containing an ether bond or an ester bond is preferable.

As the structural unit (a2) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

When the component (A1) contains the structural unit (a2), the amount of the structural unit (a2) based on the combined total of all structural units constituting the component (A1) is preferably 1 to 80 mol %, more preferably 10 to 70 mol %, still more preferably 10 to 65 mol %, and most preferably 10 to 60 mol %. When the amount of the structural unit (a2) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a2) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a2) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units, and various lithography properties such as DOF and CDU and pattern shape can be improved.

Structural Unit (a3)

The structural unit (a2) is a structural unit containing a polar group, which does not fall under the definition of the aforementioned structural units (a0), (a6) and (a1). When the component (A1) includes the structural unit (a3), the polarity of the component (A1) after exposure is further increased. Increase in the polarity contributes to improvement in terms of resolution and the like, particularly in an alkali developing process.

Examples of the polar group include —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂. Structural units that contain —COOH include structural units of (α-substituted) acrylic acid.

The structural unit (a3) is preferably a structural unit containing a hydrocarbon group in which part of the hydrogen atoms has been substituted with a polar group. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Among these, as the hydrocarbon group, an aliphatic hydrocarbon group is preferable.

Examples of the aliphatic hydrocarbon group as the hydrocarbon group include linear or branched hydrocarbon groups (preferably alkylene groups) of 1 to 10 carbon atoms, and aliphatic cyclic groups (monocyclic groups and polycyclic groups).

These aliphatic cyclic groups (monocyclic groups and polycyclic groups) can be selected appropriately from the multitude of groups that have been proposed for the resins of resist compositions designed for use with ArF excimer lasers. The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. As the aliphatic cyclic group, a group in which two or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which two or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which two or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. The aliphatic cyclic group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, and a fluorinated alkyl group of 1 to 5 carbon atoms.

The aromatic hydrocarbon group for the hydrocarbon group is a hydrocarbon group having an aromatic ring, and preferably has 5 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, still more preferably 6 to 15 carbon atoms, and most preferably 6 to 10 carbon atoms. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group. The aromatic ring included in the aromatic hydrocarbon group is the same as defined above, and specific examples include benzene, naphthalene, anthracene and phenanthrene.

Specific examples of the aromatic hydrocarbon group include a group in which two hydrogen atoms have been removed from the aforementioned aromatic ring (arylene group); a group in which two hydrogen atoms have been removed from an aromatic compound having two or more aromatic rings (biphenyl, fluorene or the like); and a group in which one hydrogen atom of the aforementioned aromatic hydrocarbon ring has been substituted with an alkylene group (a group in which one hydrogen atom has been removed from the aryl group within the aforementioned arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group). The alkylene group (alkyl chain within the arylalkyl group) preferably has 1 to 4 carbon atom, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may or may not have a substituent. For example, the hydrogen atom bonded to the aromatic ring within the aromatic hydrocarbon group may be substituted with a substituent. Examples of the substituent include an alkyl group, a halogen atom and a halogenated alkyl group.

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

As the structural unit (a3), a structural unit represented by general formula (a3-1) shown below is preferable.

In the formulae, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; P⁰ represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond; and W⁰ represents —COOH, a hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CON H₂, or —CONHCO—R^(a3) (R^(a3) represents a hydrocarbon group), provided that the hydrocarbon group may have an oxygen atom or a sulfur atom at an arbitrary position.

In the formula (a3-1), R is the same as defined above.

In the formula (a3-1), P⁰ represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond. The alkyl group for R⁰ is the same as defined for the alkyl group for R.

In the formula (a3-1), W⁰ represents a hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂, or —CONHCO—R^(a3) (R^(a3) represents a hydrocarbon group), provided that the hydrocarbon group may have an oxygen atom or a sulfur atom at an arbitrary position.

A “hydrocarbon group which has a substituent” refers to a hydrocarbon group in which at least part of the hydrogen atoms bonded to the hydrocarbon group is substituted with a substituent.

The hydrocarbon group for W⁰ or R^(a3) may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

Preferable examples of the aliphatic hydrocarbon group for W⁰ or R^(a3) include linear or branched hydrocarbon groups of 1 to 10 carbon atoms (preferably alkylene groups) and aliphatic cyclic groups (monocyclic groups and polycyclic groups), and are the same as explained above.

The aromatic hydrocarbon group for W⁰ or R^(a3) is a hydrocarbon group having at least one aromatic ring, and is the same as explained above.

W⁰ may have an oxygen atom or a sulfur atom at an arbitrary position. Here, the expression “may have an oxygen atom or a sulfur atom at an arbitrary position” means that part of the carbon atoms constituting the hydrocarbon group or the hydrocarbon group having a substituent (including the carbon atoms of the substituent part) may be substituted with an oxygen atom or a sulfur atom, or a hydrogen atom bonded to the hydrocarbon group may be substituted with an oxygen atom or a sulfur atom.

Examples of W⁰ which has an oxygen atom (O) at an arbitrary position are shown below.

In the formulae, W⁰⁰ represents a hydrocarbon group; and R^(m) represents an alkylene group of 1 to 5 carbon atoms.

In the formulae above, W⁰⁰ represents a hydrocarbon group, and is the same as defined for W⁰ in the aforementioned formula (a3-1). W⁰⁰ is preferably an aliphatic hydrocarbon group, and more preferably an aliphatic cyclic group (a monocyclic group or a polycyclic group).

R^(m) is preferably linear or branched, preferably an alkylene group of 1 to 3 carbon atoms, and more preferably a methylene group or an ethylene group.

Specific examples of preferable structural units as the structural unit (a3) include a structural unit derived from an (α-substituted) acrylate ester, and structural units represented by general formulae (a3-11) to (a3-13) shown below. Examples of the structural unit derived from an (α-substituted) acrylate ester include a structural unit in which P⁰ in the aforementioned formula (a3-1) is a single bond and W⁰ is —COOH.

In the formulae, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W⁰¹ represents an aromatic hydrocarbon group which has at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂; each of P⁰² and P⁰³ independently represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond; W⁰² represents a cyclic hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂, or —CONHCO—R^(a32) (R^(a32) represents a cyclic hydrocarbon group), provided that the hydrocarbon group may have an oxygen atom or a sulfur atom at an arbitrary position; and W⁰³ represents a chain-like hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂, or —CONHCO—R^(a33) (R^(a33) represents a chain-like alkyl group).

[Structural Unit Represented by General Formula (a3-11)]

In the formula (a3-11), R is the same as defined for R in the aforementioned formula (a3-1).

The aromatic hydrocarbon group for W⁰¹ is the same as defined for the aromatic hydrocarbon group for W⁰ in the aforementioned formula (a3-1).

Specific examples of structural units preferable as a structural unit represented by general formula (a3-11) are shown below. In the formulae shown below, R^(a) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

[Structural Unit represented by General Formula (a3-12)]

In the formula (a3-12), R is the same as defined for R in the aforementioned formula (a3-1).

P⁰² represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond, and is preferably —C(═O)—O— or a single bond. The alkyl group for R⁰ is the same as defined for the alkyl group for R.

The cyclic hydrocarbon group for W⁰² or R^(a32) is the same as defined for the aliphatic cyclic groups (monocyclic groups and polycyclic groups) and aromatic hydrocarbon groups explained above for W⁰ in the aforementioned formula (a3-1).

W⁰² or R^(a32) may have an oxygen atom or a sulfur atom at an arbitrary position, and is the same as defined for W⁰ in the aforementioned formula (a3-1).

Specific examples of structural units preferable as a structural unit represented by general formula (a3-12) are shown below. In the formulae shown below, R^(a) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

When the component (A1) includes a structural unit (a3), as the structural unit (a3), one type of structural unit may be used, or two or more types may be used.

When the component (A1) contains the structural unit (a3), the amount of the structural unit (a3) based on the combined total of all structural units constituting the component (A1) is preferably 0 to 85 mol %, and more preferably 0 to 80 mol %. When the amount of the structural unit (a3) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a3) (effect of improving resolution, lithography properties and pattern shape) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a3) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

Structural Unit (a4)

The structural unit (a4) is a structural unit containing a non-acid dissociable, aliphatic polycyclic group.

In the structural unit (a4), examples of this polycyclic group include the same polycyclic groups as those described above in relation to the aforementioned structural unit (a1), and any of the multitude of conventional polycyclic groups used within the resin component of resist compositions for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

In consideration of industrial availability and the like, at least one polycyclic group selected from amongst a tricyclodecyl group, adamantyl group, tetracyclododecyl group, isobornyl group, and norbornyl group is particularly desirable. These polycyclic groups may be substituted with a linear or branched alkyl group of 1 to 5 carbon atoms.

Specific examples of the structural unit (a4) include units with structures represented by general formulas (a4-1) to (a4-5) shown below.

In the formulae, R is the same as defined above.

When the structural unit (a4) is included in the component (A1), the amount of the structural unit (a4) based on the combined total of all the structural units that constitute the component (A1) is preferably within the range from 1 to 30 mol %, and more preferably from 10 to 20 mol %.

In the resist composition of the present invention, the component (A) contains a resin component (A1) having the aforementioned structural units (a0), (a6) and (a1).

Specific examples of the component (A1) include a polymeric compound consisting of a structural unit (a0), a structural unit (a1), a structural unit (a6) and a structural unit (a2); a polymeric compound consisting of a structural unit (a0), a structural unit (a1), a structural unit (a6) and a structural unit (a3); a polymeric compound consisting of a structural unit (a0), a structural unit (a1), a structural unit (a6), a structural unit (a2) and a structural unit (a3); and a polymeric compound consisting of a structural unit (a0), a structural unit (a1), a structural unit (a6), a structural unit (a2), a structural unit (a3) and a structural unit (a4).

In the component (A), as the component (A1), one type may be used alone, or two or more types may be used in combination.

In the component (A), the amount of the component (A1) based on the total weight of the component (A) is preferably 25% by weight or more, more preferably 50% by weight or more, still more preferably 75% by weight or more, and most preferably 100% by weight. When the amount of the component (A1) is 25% by weight or more, the effects of the present invention are further improved.

The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the component (A1) is not particularly limited, but is preferably 1,000 to 50,000, more preferably 1,500 to 30,000, and most preferably 2,000 to 20,000. When the weight average molecular weight is no more than the upper limit of the above-mentioned range, the resist composition exhibits a satisfactory solubility in a resist solvent. On the other hand, when the weight average molecular weight is at least as large as the lower limit of the above-mentioned range, dry etching resistance and the cross-sectional shape of the resist pattern becomes satisfactory.

Further, the dispersity (Mw/Mn) is not particularly limited, but is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.0 to 2.5. Here, Mn is the number average molecular weight.

The component (A) can be obtained, for example, by a conventional radical polymerization or the like of the monomers corresponding with each of the structural units, using a radical polymerization initiator such as azobisisobutyronitrile (AlBN).

Furthermore, in the component (A), by using a chain transfer agent such as HS—CH₂—CH₂—CH₂—C(CF₃)₂—OH, a —C(CF₃)₂—OH group can be introduced at the terminals of the component (A1). Such a copolymer having introduced a hydroxyalkyl group in which some of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is effective in reducing developing defects and LER (line edge roughness: unevenness of the side walls of a line pattern).

As the monomers which yield the corresponding structural units, commercially available monomers may be used, or the monomers may be synthesized by a conventional method.

The component (A) may contain a base component other than the component (A1) (hereafter, such base component is referred to as “component (A2)”), as long as the effects of the present invention are not impaired.

As the component (A2) a low molecular weight compound that have a molecular weight of at least 500 and less than 4,000, contains a hydrophilic group, and also contains an acid dissociable group described above in connection with the component (A1), can be used. Specific examples include compounds containing a plurality of phenol skeletons in which part or all of the hydrogen atoms within hydroxyl groups have been substituted with the aforementioned acid dissociable groups.

Examples of the low-molecular weight compound include low molecular weight phenolic compounds in which a portion of the hydroxyl group hydrogen atoms have been substituted with an aforementioned acid dissociable group, and these types of compounds are known, for example, as sensitizers or heat resistance improvers for use in non-chemically amplified g-line or i-line resists.

Examples of these low molecular weight phenol compounds include bis(4-hydroxyphenyl)methane, bis(2,3,4-trihydroxyphenyl)methane, 2-(4-hydroxyphenyl)-2-(4′-hydroxyphenyl)propane, 2-(2,3,4-trihydroxyphenyl)-2-(2′,3′,4′-trihydroxyphenyl)propane, tris(4-hydroxyphenyl)methane, bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-3-methylphenyl)-3,4-dihydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-4-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-3,4-dihydroxyphenylmethane, 1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene, and dimers, trimers, tetramers, pentamers and hexamers of formalin condensation products of phenols such as phenol, m-cresol, p-cresol and xylenol. Needless to say, the low molecular weight phenol compound is not limited to these examples. In particular, a phenol compound having 2 to 6 triphenylmethane skeletons is preferable in terms of resolution and line edge roughness (LER). Also, there are no particular limitations on the acid dissociable group, and suitable examples include the groups described above.

In the resist composition of the present invention, the amount of the component (A) can be appropriately adjusted depending on the thickness of the resist film to be formed, and the like.

<Optional Components>

[Component (B)]

The resist composition of the present invention may further include an acid generator component (B) (hereafter, referred to as “component (B)”) which generates acid upon exposure.

In the resist composition of the present invention, as the component (B), there is no particular limitation, and any of the known acid generators used in conventional chemically amplified resist compositions can be used.

Examples of these acid generators are numerous, and include onium salt acid generators such as iodonium salts and sulfonium salts; oxime sulfonate acid generators; diazomethane acid generators such as bisalkyl or bisaryl sulfonyl diazomethanes and poly(bis-sulfonyl)diazomethanes; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators.

As an onium salt acid generator, a compound represented by general formula (b-1) or (b-2) shown below can be used.

In the formulae, R¹″ to R³″, R⁵″ and R⁶″ each independently represents an aryl group which may have a substituent, an alkyl group which may have a substituent or an alkenyl group which may have a substituent, provided that, in formula (b-1), two of R¹″ to R³″ may be mutually bonded to form a ring with the sulfur atom; and R⁴″ represents an alkyl group which may have a substituent, a halogenated alkyl group which may have a substituent, an aryl group which may have a substituent or an alkenyl group which may have a substituent.

R¹″ to R³″ in formula (b-1) and R⁵″ and R⁶″ in formula (b-2) are respectively the same as defined for R¹″ to R³″ in formula (m-1) and R⁵″ and R⁶″ in formula (m-2) explained above in relation to the structural unit (a6-0-2).

In formulae (b-1) and (b-2), R⁴″SO₃ ⁻ is the same as defined for R⁴″SO₃ ⁻ explained above in relation to V⁻ in the aforementioned formula (a6-0-1).

As the component (B), one type of these acid generators may be used alone, or two or more types may be used in combination.

When the resist composition of the present invention contains the component (B), the amount of the component (B) relative to 100 parts by weight of the component (A) is preferably within a range from 0.5 to 60 parts by weight, more preferably from 1 to 50 parts by weight, and still more preferably from 1 to 40 parts by weight. When the amount of the component (B) is within the above-mentioned range, formation of a resist pattern can be satisfactorily performed. Further, by virtue of the above-mentioned range, when each of the components are dissolved in an organic solvent, a uniform solution can be obtained and the storage stability becomes satisfactory.

<Optional Components>

[Basic Compound (D)]

It is preferable that the resist composition of the present invention further includes a basic compound (D) (hereafter referred to as the component (D)) as an optional component.

In the present invention, the component (D) functions as an acid diffusion control agent, i.e., a quencher which traps the acid generated from the component (A), the component (B) and the like upon exposure. In the present invention, a “basic compound” refers to a compound which is basic relative to the component (A) or the component (B).

In the present invention, the component (D) may be a basic compound (D1) (hereafter, referred to as “component (D1)”) which has a cation moiety and an anion moiety, or a basic compound (D2) (hereafter, referred to as “component (D2)”) which does not fall under the definition of component (D1).

{Component (D1)}

The component (D1) is a basic compound composed of a cation moiety and an anion moiety. The basic compound traps acid (strong acid) generated from the component (A) and the component (B) by a salt exchange.

Specific examples of the component (D1) include a compound (D11) represented by general formula (d11), a compound (D12) represented by general formula (d12) and a compound (D13) represented by general formula (d13).

In the formulae, R¹⁴ represents a hydrocarbon group which may have a substituent; Z^(2c) represents a hydrocarbon group of 1 to 30 carbon atoms which may have a substituent, provided that the carbon atom adjacent to S is not substituted with fluorine; R¹⁵ represents an organic group; Y⁵ represents a linear, branched or cyclic alkylene group or an arylene group; Rf³ represents a hydrocarbon group containing a fluorine atom; and each M⁺ independently represents a sulfonium cation or an iodonium cation.

(Compound (D11))

Anion Moiety

In formula (d11), R¹⁴represents a hydrocarbon group which may have a substituent.

The hydrocarbon group for R¹⁴ which may have a substituent may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and the same group as X³ in the formula X³-Q′- described above as the substituent for R⁴″ in general formula “R⁴″SO₃ ⁻” in the explanation of the structural unit (a6-0-1) can be mentioned.

Among these, as the hydrocarbon group for R¹⁴ which may have a substituent, an aromatic hydrocarbon group which may have a substituent or an aliphatic cyclic group which may have a substituent is preferable, and a phenyl group or a naphthyl group which may have a substituent, or a group in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane is more preferable.

As the hydrocarbon group for R¹⁴ which may have a substituent, a linear or branched alkyl group or a fluorinated alkyl group is also preferable.

The linear or branched alkyl group for R¹⁴ preferably has 1 to 10 carbon atoms, and specific examples thereof include a linear alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl or a decyl group, and a branched alkyl group such as a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group or a 4-methylpentyl group.

The fluorinated alkyl group for R¹⁴ may be either chain-like or cyclic, but is preferably linear or branched.

The fluorinated alkyl group preferably has 1 to 11 carbon atoms, more preferably 1 to 8, and still more preferably 1 to 4. Specific examples include a group in which part or all of the hydrogen atoms constituting a linear alkyl group (such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group or a decyl group) have been substituted with fluorine atom(s), and a group in which part or all of the hydrogen atoms constituting a branched alkyl group (such as a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group or a 3-methylbutyl group) have been substituted with fluorine atom(s).

The fluorinated alkyl group for R¹⁴ may contain an atom other than fluorine. Examples of the atom other than fluorine include an oxygen atom, a carbon atom, a hydrogen atom, an oxygen atom, a sulfur atom and a nitrogen atom.

Among these, as the fluorinated alkyl group for R¹⁴, a group in which part or all of the hydrogen atoms constituting a linear alkyl group have been substituted with fluorine atom(s) is preferable, and a group in which all of the hydrogen atoms constituting a linear alkyl group have been substituted with fluorine atoms (i.e., a perfluoroalkyl group) is more preferable.

Specific examples of preferable anion moieties for the compound (D11) are shown below.

Cation Moiety

In formula (d11), M⁺ represents an organic cation.

The organic cation for M⁺ is not particularly limited, and an organic cation conventionally known as the cation moiety of a photo-decomposable base used as a quencher for a resist composition or the cation moiety of an onium salt acid generator for a resist composition can be used. The organic cation is the same as defined for (m-1) and (m-2) in the aforementioned formula (a6-0-2).

As the compound (D11), one type of compound may be used alone, or two or more types of compounds may be used in combination.

(Compound (D12))

Anion Moiety

In formula (d12), Z^(2c) represents a hydrocarbon group of 1 to 30 carbon atoms which may have a substituent.

The hydrocarbon group of 1 to 30 carbon atoms for Z^(2c) which may have a substituent may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and is the same as defined for R¹⁴ in the aforementioned formula (d11).

Among these, as the hydrocarbon group for Z^(2c) which may have a substituent, an aliphatic cyclic group which may have a substituent is preferable, and a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane, tetracyclododecane or camphor (which may have a substituent) is more preferable.

The substituent for the hydrocarbon group represented by Z^(2c) is the same as defined for the substituent for R⁴″ in “R⁴″SO₃ ⁻” explained above in relation to V⁻ in the aforementioned general formula (a6-0-1). Specific examples include a halogen atom, a hetero atom, an alkyl group, and a group represented by the formula X³-Q′- (in the formula, Q′ represents a divalent linking group containing an oxygen atom; and X³ represents a hydrocarbon group of 3 to 30 carbon atoms which may have a substituent). However, in Z^(2c), the carbon adjacent to the S atom within SO₃ ⁻ has no fluorine atom as a substituent. By virtue of SO₃ ⁻ having no fluorine atom adjacent thereto, the anion of the compound (D12) becomes an appropriately weak acid anion, thereby improving the quenching ability of the component (D).

Specific examples of preferable anion moieties for the compound (D12) are shown below.

Cation Moiety

In formula (d12), M⁺ is the same as defined for M⁺ in the aforementioned formula (d11).

As the compound (D12), one type of compound may be used alone, or two or more types of compounds may be used in combination.

(Compound (D13))

Anion Moiety

In formula (d13), R¹⁵ represents an organic group.

The organic group for R¹⁵ is not particularly limited, and an alkyl group, an alkoxy group, —13 C(═O)—C(R^(C2))═CH₂ (R^(C2) represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms) or —O—C(═O)—R^(C3) (R^(C3) represents a hydrocarbon group) is preferable.

The alkyl group for R¹⁵ is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group. Part of the hydrogen atoms within the alkyl group for R¹⁵ may be substituted with a hydroxy group, a cyano group or the like.

The alkoxy group for R¹⁵ is preferably an alkoxy group of 1 to 5 carbon atoms, and specific examples thereof include a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group and a tert-butoxy group. Among these, a methoxy group and an ethoxy group are particularly desirable.

In —o—C(═O)—C(R^(C2))═CH₂, R^(C2) represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group of 1 to 5 carbon atoms for R^(C2) is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group and a neopentyl group.

The halogenated alkyl group for R^(C2) is a group in which part or all of the hydrogen atoms of the aforementioned alkyl group of 1 to 5 carbon atoms has been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

As R^(C2), a hydrogen atom, an alkyl group of 1 to 3 carbon atoms or a fluorinated alkyl group of 1 to 3 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly desirable in terms of industrial availability.

In —O—C(═O)—R^(C3), R^(C3) represents a hydrocarbon group.

The hydrocarbon group for R^(C3) may be either an aromatic hydrocarbon group or an aliphatic hydrocarbon group. Specific examples of the hydrocarbon group for R^(C3) include the same hydrocarbon groups as those described for R¹⁴ in the aforementioned formula (d11).

Among these, as the hydrocarbon group for R^(C3), an alicyclic group (e.g., a group in which one or more hydrogen atoms have been removed from a cycloalkane such as cyclopentane, cyclohexane, adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane) or an aromatic group (e.g., a phenyl group or a naphthyl group) is preferable. When R^(C3) is an alicyclic group, the resist composition can be satisfactorily dissolved in an organic solvent, thereby improving the lithography properties.

Among these, as R¹⁵, —O—C(═O)—C(R^(C2)′)═CH₂ (R^(C2)′ represents a hydrogen atom or a methyl group) or —O—C(═O)—R^(C3)′ (R^(C3)′ represents an aliphatic cyclic group) is preferable.

In formula (d13), Y¹ represents a linear, branched or cyclic alkylene group or an arylene group.

Examples of the linear or branched alkylene group for Y⁵ include the “linear or branched aliphatic hydrocarbon group” described above as the divalent linking group for Y¹ and Y² in the aforementioned formula (a0-1).

Examples of the cyclic alkylene group for Y⁵ include the “cyclic aliphatic hydrocarbon group” described above as the divalent linking group for Y¹ and Y² in the aforementioned formula (a0-1).

Examples of the arylene group for Y⁵ include groups in which two hydrogen atoms have been removed from the aromatic hydrocarbon ring described above as the divalent linking group for Y¹ and Y² in the aforementioned formula (a0-1).

Among these, as Y⁵, an alkylene group is preferable, a linear or branched alkylene group is more preferable, and a methylene group or an ethylene group is still more preferable.

In formula (d13), Rf³ represents a hydrocarbon group containing a fluorine atom.

The hydrocarbon group containing a fluorine atom for Rf³ is preferably a fluorinated alkyl group, and more preferably the same fluorinated alkyl groups as those described above for R¹⁴.

Specific examples of preferable anion moieties for the compound (D13) are shown below.

Cation Moiety

In formula (d13), M⁺ is the same as defined for M⁺ in the aforementioned formula (d11).

As the compound (D13), one type of compound may be used alone, or two or more types of compounds may be used in combination.

As the compounds (D11) to (D13), commercially available compounds may be used, or the compounds may be synthesized by a conventional method.

The production methods of the compounds (D11) and (D12) are not particularly limited, and the compounds (D11) and (D12) can be produced by conventional methods.

The production method of the compound (D13) is not particularly limited. For example, in the case where R¹⁵ in formula (d13) is a group having an oxygen atom on the terminal thereof which is bonded to Y⁵, the compound (D13) can be produced by reacting a compound (i-1) represented by general formula (i-1) shown below with a compound (i-2) represented by general formula (i-2) shown below to obtain a compound (i-3) represented by general formula (i-3), and reacting the compound (i-3) with a compound Z⁻M⁺ having the desired cation M⁺, thereby obtaining the objective compound.

In the formulae, R¹⁵, Y⁵, Rf³ and M⁺ are respectively the same as defined for R¹⁵, Y⁵, Rf³ and M⁺ in the aforementioned general formula (d13); Z⁻ represents a group in which the terminal oxygen atom has been removed from R¹⁵; and Z⁻ represents a counteranion.

Firstly, the compound (i-1) is reacted with the compound (i-2), to thereby obtain the compound (i-3).

In formula (i-1), R^(5a) represents a group in which the terminal oxygen atom has been removed from R¹⁵. In formula (i-2), Y⁵ and Rf³ are the same as defined above.

As the compound (i-1) and the compound (i-2), commercially available compounds may be used, or the compounds may be synthesized.

The method for reacting the compound (i-1) with the compound (i-2) to obtain the compound (i-3) is not particularly limited, but can be performed, for example, by reacting the compound (i-1) with the compound (i-2) in an organic solvent in the presence of an appropriate acidic catalyst, followed by washing and recovering the reaction mixture.

The acidic catalyst used in the above reaction is not particularly limited, and examples thereof include toluenesulfonic acid and the like. The amount of the acidic catalyst is preferably 0.05 to 5 moles, per 1 mole of the compound (i-2).

As the organic solvent used in the above reaction, any organic solvent which is capable of dissolving the raw materials, i.e., the compound (i-1) and the compound (i-2) can be used, and specific examples thereof include toluene and the like. The amount of the organic solvent is preferably 0.5 to 100 parts by weight, more preferably 0.5 to 20 parts by weight, relative to the amount of the compound (i-1). As the solvent, one type may be used alone, or two or more types may be used in combination.

In general, the amount of the compound (i-2) used in the above reaction is preferably 0.5 to 5 moles per 1 mole of the compound (i-1), and more preferably 0.8 to 4 moles per 1 mole of the compound (i-1).

The reaction time depends on the reactivity of the compounds (i-1) and (i-2), the reaction temperature or the like. However, in general, the reaction time is preferably 1 to 80 hours, and more preferably 3 to 60 hours.

The reaction temperature in the above reaction is preferably 20 to 200° C., and more preferably 20 to 150° C.

Next, the obtained compound (i-3) is reacted with the compound (i-4), thereby obtaining the compound (D13).

In formula (i-4), M⁺ is the same as defined above, and Z⁻ represents a counteranion.

The method for reacting the compound (i-3) with the compound (i-4) to obtain the compound (d1-3) is not particularly limited, but can be performed, for example, by dissolving the compound (i-3) in an organic solvent and water in the presence of an appropriate alkali metal hydroxide, followed by addition of the compound (i-4) and stirring.

The alkali metal hydroxide used in the above reaction is not particularly limited, and examples thereof include sodium hydroxide, potassium hydroxide and the like. The amount of the alkali metal hydroxide is preferably 0.3 to 3 moles, per 1 mole of the compound (i-3).

Examples of the organic solvent used in the above reaction include dichloromethane, chloroform, ethyl acetate and the like. The amount of the organic solvent is preferably 0.5 to 100 parts by weight, and more preferably 0.5 to 20 parts by weight, relative to the weight of the compound (i-3). As the solvent, one type may be used alone, or two or more types may be used in combination.

In general, the amount of the compound (i-4) used in the above reaction is preferably 0.5 to 5 moles per I mole of the compound (i-3), and more preferably 0.8 to 4 moles per 1 mole of the compound (i-3).

The reaction time depends on the reactivity of the compounds (i-3) and (i-4), the reaction temperature or the like. However, in general, the reaction time is preferably 1 to 80 hours, and more preferably 3 to 60 hours.

The reaction temperature in the above reaction is preferably 20 to 200° C., and more preferably 20 to 150° C.

After the reaction, the compound (D13) contained in the reaction mixture may be separated and purified. The separation and purification can be conducted by a conventional method. For example, any one of concentration, solvent extraction, distillation, crystallization, recrystallization and chromatography can be used alone, or two or more of these methods may be used in combination.

The structure of the compound obtained in the manner described above can be confirmed by a general organic analysis method such as ¹H-nuclear magnetic resonance (NMR) spectrometry, ¹³C-NMR spectrometry, ¹⁹F-NMR spectrometry, infrared absorption (IR) spectrometry, mass spectrometry (MS), elementary analysis and X-ray diffraction analysis.

{Component (D2)}

The component (D2) is a basic compound which does not fall under the definition of the aforementioned component (D1).

The component (D2) is not particularly limited, as long as it is a compound which is basic relative to the component (A) or the component (B), so as to functions as an acid diffusion control agent, i.e., a quencher which traps the acid generated from the component (A) or the component (B) upon exposure, and does not fall under the definition of the component (D1). As the component (D2), any of the conventionally known compounds may be selected for use. Examples thereof include an aliphatic amine and an aromatic amine. Among these, an aliphatic amine is preferable, and a secondary aliphatic amine or tertiary aliphatic amine is particularly desirable.

An aliphatic amine is an amine having one or more aliphatic groups, and the aliphatic groups preferably have 1 to 12 carbon atoms.

Examples of these aliphatic amines include amines in which at least one hydrogen atom of ammonia (NH₃) has been substituted with an alkyl group or hydroxyalkyl group of no more than 20 carbon atoms (i.e., alkylamines or alkylalcoholamines), cyclic amines, and other aliphatic amines.

The alkyl group within the alkylamine may be linear, branched or cyclic.

When the alkyl group is linear or branched, the alkyl group preferably has 2 to 20 carbon atoms, and more preferably 2 to 8 carbon atoms.

When the alkyl group is cyclic (i.e., a cycloalkyl group), the number of carbon atoms is preferably 3 to 30, more preferably 3 to 20, still more preferably 3 to 15, still more preferably 4 to 12, and most preferably 5 to 10. The alkyl group may be monocyclic or polycyclic. Examples thereof include groups in which one or more of the hydrogen atoms have been removed from a monocycloalkane; and groups in which one or more of the hydrogen atoms have been removed from a polycycloalkane such as a bicycloalkane, a tricycloalkane, or a tetracycloalkane. Specific examples of the monocycloalkane include cyclopentane and cyclohexane. Specific examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

As the alkyl group within the hydroxyalkyl group of the alkylalcoholamine, the same alkyl groups as those described above for the alkylamines can be mentioned.

Specific examples of alkylamines include monoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, and n-decylamine; dialkylamines such as diethylamine, di-n-propylamine, di-n-heptylamine, di-n-octylamine, and dicyclohexylamine; trialkylamines such as trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-hexylamine, tri-n-pentylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decanylamine, and tri-n-dodecylamine.

Specific examples of alkylalcoholamines include diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, di-n-octanolamine, tri-n-octanolamine, stearyldiethanolamine and lauryldiethanolamine.

Among these, trialkylamines of 5 to 10 carbon atoms are preferable, and tri-n-pentylamine and tri-n-octylamine are particularly desirable.

Examples of the cyclic amine include heterocyclic compounds containing a nitrogen atom as a hetero atom. The heterocyclic compound may be a monocyclic compound (aliphatic monocyclic amine), or a polycyclic compound (aliphatic polycyclic amine).

Specific examples of the aliphatic monocyclic amine include piperidine, and piperazine.

The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, and specific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene, 1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and 1,4-diazabicyclo[2.2.2]octane.

Examples of other aliphatic amines include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine, tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine and triethanolamine triacetate.

Examples of aromatic amines include aniline, pyridine, 4-dimethylaminopyridine, pyrrole, indole, pyrazole, imidazole and derivatives thereof, as well as diphenylamine, triphenylamine, tribenzylamine, 2,6-diisopropylaniline and N-tert-butoxycarbonylpyrrolidine.

As the component (D2), one type of compound may be used, or two or more types of compounds may be used in combination.

In the resist composition of the present invention, in terms of achieving excellent lithography properties such as roughness, it is preferable to include the component (D1) as the component (D). As the component (D), one type of the compounds (D11) to (D13) may be used, or two or more types may be used in combination. Of these, it is preferable to include the component (D12).

The amount of the component (D1) relative to 100 parts by weight of the component (A) is preferably within a range from 0.5 to 10.0 parts by weight, more preferably from 0.5 to 8.0 parts by weight, still more preferably from 1.0 to 8.0 parts by weight, and most preferably from 1.5 to 5.5 parts by weight. When the amount of the component (D) is at least as large as the lower limit of the above-mentioned range, various lithography properties such as resolution, roughness and exposure latitude are improved. Further, a resist pattern having an excellent shape can be obtained. On the other hand, when the amount of the component (D) is no more than the upper limit of the above-mentioned range, sensitivity can be maintained at a satisfactory level, and through-top becomes excellent.

When the resist composition of the present invention contains the component (D2), the amount of the component (D2) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A). When the amount of the component (D) is within the above-mentioned range, the shape of the resist pattern and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer are improved.

[Component (E)]

Furthermore, in the resist composition for immersion exposure according to the present invention, for preventing any deterioration in sensitivity, and improving the resist pattern shape and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer, at least one compound (E) (hereafter referred to as “component (E)”) selected from the group consisting of organic carboxylic acids, and phosphorus oxo acids and derivatives thereof can be added.

Examples of suitable organic carboxylic acids include acetic acid, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid.

Examples of phosphorus oxo acids include phosphoric acid, phosphonic acid and phosphinic acid. Among these, phosphonic acid is particularly desirable.

Examples of oxo acid derivatives include esters in which a hydrogen atom within the above-mentioned oxo acids is substituted with a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group of 1 to 5 carbon atoms and an aryl group of 6 to 15 carbon atoms.

Examples of phosphoric acid derivatives include phosphoric acid esters such as di-n-butyl phosphate and diphenyl phosphate.

Examples of phosphonic acid derivatives include phosphonic acid esters such as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid, diphenyl phosphonate and dibenzyl phosphonate.

Examples of phosphinic acid derivatives include phenylphosphinic acid and phosphinic acid esters.

As the component (E), one type may be used alone, or two or more types may be used in combination.

The component (E) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A).

If desired, other miscible additives can also be added to the resist composition of the present invention. Examples of such miscible additives include additive resins for improving the performance of the resist film, surfactants for improving the applicability, dissolution inhibitors, plasticizers, stabilizers, colorants, halation prevention agents, and dyes.

[Component (S)]

The resist composition for immersion exposure according to the present invention can be prepared by dissolving the materials for the resist composition in an organic solvent (hereafter, frequently referred to as “component (S)”).

The component (S) may be any organic solvent which can dissolve the respective components to give a uniform solution, and one or more kinds of any organic solvent can be appropriately selected from those which have been conventionally known as solvents for a chemically amplified resist.

Examples thereof include lactones such as γ-butyrolactone;

ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl-n-pentyl ketone, methyl isopentyl ketone, and 2-heptanone;

polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol;

compounds having an ester bond, such as ethylene glycol monoacetate, diethylene glycol monoacetate, propylene glycol monoacetate, and dipropylene glycol monoacetate; polyhydric alcohol derivatives including compounds having an ether bond, such as a monoalkylether (e.g., monomethylether, monoethylether, monopropylether or monobutylether) or monophenylether of any of these polyhydric alcohols or compounds having an ester bond (among these, propylene glycol monomethyl ether acetate (PGMEA) and propylene glycol monomethyl ether (PGME) are preferable); cyclic ethers such as dioxane; esters such as methyl lactate, ethyl lactate (EL), methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate;

and aromatic organic solvents such as anisole, ethylbenzylether, cresylmethylether, diphenylether, dibenzylether, phenetole, butylphenylether, ethylbenzene, diethylbenzene, pentylbenzene, isopropylbenzene, toluene, xylene, cymene and mesitylene.

These solvents can be used individually, or in combination as a mixed solvent.

Among these, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME) and ethyl lactate (EL) are preferable.

Further, among the mixed solvents, a mixed solvent obtained by mixing PGMEA with a polar solvent is preferable. The mixing ratio (weight ratio) of the mixed solvent can be appropriately determined, taking into consideration the compatibility of the PGMEA with the polar solvent, but is preferably in the range of 1:9 to 9:1, more preferably from 2:8 to 8:2. For example, when EL is mixed as the polar solvent, the PGMEA:EL weight ratio is preferably from 1:9 to 9:1, and more preferably from 2:8 to 8:2. Alternatively, when PGME is mixed as the polar solvent, the PGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3. Alternatively, when PGME and cyclohexanone is mixed as the polar solvent, the PGMEA:(PGME +cyclohexanone) weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3.

Further, as the component (S), a mixed solvent of γ-butyrolactone with PGMEA, EL or the aforementioned mixed solvent of PGMEA with a polar solvent, is also preferable. The mixing ratio (former:latter) of such a mixed solvent is preferably from 70:30 to 95:5.

The amount of the organic solvent is not particularly limited, and is appropriately adjusted to a concentration which enables coating of a coating solution to a substrate, depending on the thickness of the coating film. In general, the organic solvent is used in an amount such that the solid content of the resist composition becomes within the range from 1 to 20% by weight, and preferably from 2 to 15% by weight.

The resist composition of the present invention exhibits excellent lithography properties such as resolution and exposure latitude in the formation of a resist pattern, and is capable of forming an excellent resist pattern with reduced roughness. The reasons why these effects can be achieved are presumed as follows.

In the resist composition of the present invention, the component (A1) includes the structural unit (a6) which generates acid upon exposure. Therefore, when a resist film is formed using the resist composition, and the resist film is subjected to a selective exposure, at exposed portions, acid is uniformly generated from the structural unit (a6) which is uniformly distributed within the resist film. As a result, it is presumed that, the acid decomposable groups within the component (A1) at exposed portions are likely to be uniformly decomposed, thereby improving the lithography properties such as resolution as compared to a resist composition using a conventional acid generator.

Further, by virtue of the the Tg of the entire resin is increased, thereby enabling to shorten the diffusion length of acid and achieve excellent lithography properties. Furthermore, by virtue of the structural unit (a0) having a branched chain, the solubility is improved, and hence, optimization of the resin depending on the lithography conditions becomes possible, thereby enabling formation of a resist pattern with excellent lithography properties.

<<Method of Forming a Resist Pattern>>

The method of forming a resist pattern according to the present invention includes: forming a resist film on a substrate using a resist composition of the present invention; conducting exposure of the resist film; and developing the resist film to form a resist pattern.

The method for forming a resist pattern according to the present invention can be performed, for example, as follows.

Firstly, a resist composition of the present invention is applied to a substrate using a spinner or the like, and a bake treatment (post applied bake (PAB)) is conducted at a temperature of 80 to 150° C. for 40 to 120 seconds, preferably 60 to 90 seconds, to form a resist film.

Following selective exposure of the thus formed resist film, either by exposure through a mask having a predetermined pattern formed thereon (mask pattern) using an exposure apparatus such as an ArF exposure apparatus, an electron beam lithography apparatus or an EUV exposure apparatus, or by patterning via direct irradiation with an electron beam without using a mask pattern, baking treatment (post exposure baking (PEB)) is conducted under temperature conditions of 80 to 150° C. for 40 to 120 seconds, and preferably 60 to 90 seconds.

Next, the resist film is subjected to a developing treatment.

The developing treatment is conducted using an alkali developing solution in the case of an alkali developing process, and a developing solution containing an organic solvent (organic developing solution) in the case of a solvent developing process.

After the developing treatment, it is preferable to conduct a rinse treatment. The rinse treatment is preferably conducted using pure water in the case of an alkali developing process, and a rinse solution containing an organic solvent in the case of a solvent developing process.

In the case of a solvent developing process, after the developing treatment or the rinsing, the developing solution or the rinse liquid remaining on the pattern can be removed by a treatment using a supercritical fluid.

After the developing treatment or the rinse treatment, drying is conducted. If desired, bake treatment (post bake) can be conducted following the developing. In this manner, a resist pattern can be obtained.

The substrate is not specifically limited and a conventionally known substrate can be used. For example, substrates for electronic components, and such substrates having wiring patterns formed thereon can be used. Specific examples of the material of the substrate include metals such as silicon wafer, copper, chromium, iron and aluminum; and glass. Suitable materials for the wiring pattern include copper, aluminum, nickel, and gold.

Further, as the substrate, any one of the above-mentioned substrates provided with an inorganic and/or organic film on the surface thereof may be used. As the inorganic film, an inorganic antireflection film (inorganic BARC) can be used. As the organic film, an organic antireflection film (organic BARC) and an organic film such as a lower-layer organic film used in a multilayer resist method can be used.

Here, a “multilayer resist method” is method in which at least one layer of an organic film (lower-layer organic film) and at least one layer of a resist film (upper resist film) are provided on a substrate, and a resist pattern formed on the upper resist film is used as a mask to conduct patterning of the lower-layer organic film. This method is considered as being capable of forming a pattern with a high aspect ratio. More specifically, in the multilayer resist method, a desired thickness can be ensured by the lower-layer organic film, and as a result, the thickness of the resist film can be reduced, and an extremely fine pattern with a high aspect ratio can be formed.

The multilayer resist method is broadly classified into a method in which a double-layer structure consisting of an upper-layer resist film and a lower-layer organic film is formed (double-layer resist method), and a method in which a multilayer structure having at least three layers consisting of an upper-layer resist film, a lower-layer organic film and at least one intermediate layer (thin metal film or the like) provided between the upper-layer resist film and the lower-layer organic film (triple-layer resist method).

The wavelength to be used for exposure is not particularly limited and the exposure can be conducted using radiation such as ArF excimer laser, KrF excimer laser,

F₂ excimer laser, extreme ultraviolet rays (EUV), vacuum ultraviolet rays (VUV), electron beam (E13), X-rays, and soft X-rays. The resist composition of the present invention is effective to KrF excimer laser, ArF excimer laser, ES and EUV

The exposure of the resist film can be either a general exposure (dry exposure) conducted in air or an inert gas such as nitrogen, or immersion exposure (immersion lithography).

In immersion lithography, the region between the resist film and the lens at the lowermost point of the exposure apparatus is pre-filled with a solvent (immersion medium) that has a larger refractive index than the refractive index of air, and the exposure (immersion exposure) is conducted in this state.

The immersion medium preferably exhibits a refractive index larger than the refractive index of air but smaller than the refractive index of the resist film to be exposed. The refractive index of the immersion medium is not particularly limited as long at it satisfies the above-mentioned requirements.

Examples of this immersion medium which exhibits a refractive index that is larger than the refractive index of air but smaller than the refractive index of the resist film include water, fluorine-based inert liquids, silicon-based solvents and hydrocarbon-based solvents.

Specific examples of the fluorine-based inert liquids include liquids containing a fluorine-based compound such as C₃HCl₂F₅, C₄F₉OCH₃, C₄F₉OC₂H₅ or C₅H₃F₇ as the main component, which have a boiling point within a range from 70 to 180° C. and preferably from 80 to 160° C. A fluorine-based inert liquid having a boiling point within the above-mentioned range is advantageous in that the removal of the immersion medium after the exposure can be conducted by a simple method.

As a fluorine-based inert liquid, a perfluoroalkyl compound in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is particularly desirable. Examples of these perfluoroalkyl compounds include perfluoroalkylether compounds and perfluoroalkylamine compounds.

Specifically, one example of a suitable perfluoroalkylether compound is perfluoro(2-butyl-tetrahydrofuran) (boiling point 102° C.), and an example of a suitable perfluoroalkylamine compound is perfluorotributylamine (boiling point 174° C.).

As the immersion medium, water is preferable in terms of cost, safety, environment and versatility.

As an example of the alkali developing solution used in an alkali developing process, a 0.1 to 10% by weight aqueous solution of tetramethylammonium hydroxide (TMAH) can be given.

As the organic solvent contained in the organic developing solution used in a solvent developing process, any of the conventional organic solvents can be used which are capable of dissolving the component (A) (prior to exposure). Specific examples of the organic solvent include polar solvents such as ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents, and hydrocarbon solvents.

If desired, the organic developing solution may have a conventional additive blended. Examples of the additive include surfactants. The surfactant is not particularly limited, and for example, an ionic or non-ionic fluorine and/or silicon surfactant can be used.

When a surfactant is added, the amount thereof based on the total amount of the organic developing solution is generally 0.001 to 5% by weight, preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% by weight.

The developing treatment can be performed by a conventional developing method. Examples thereof include a method in which the substrate is immersed in the developing solution for a predetermined time (a dip method), a method in which the developing solution is cast up on the surface of the substrate by surface tension and maintained for a predetermined period (a puddle method), a method in which the developing solution is sprayed onto the surface of the substrate (spray method), and a method in which the developing solution is continuously ejected from a developing solution ejecting nozzle while scanning at a constant rate to apply the developing solution to the substrate while rotating the substrate at a constant rate (dynamic dispense method).

As the organic solvent contained in the rinse liquid used in the rinse treatment after the developing treatment in the case of a solvent developing process, any of the aforementioned organic solvents contained in the organic developing solution can be used which hardly dissolves the resist pattern. In general, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents is used. Among these, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents and amide solvents is preferable, more preferably at least one solvent selected from the group consisting of alcohol solvents and ester solvents, and an alcohol solvent is particularly desirable.

The rinse treatment using a rinse liquid (washing treatment) can be conducted by a conventional rinse method. Examples of the rinse method include a method in which the rinse liquid is continuously applied to the substrate while rotating it at a constant rate (rotational coating method), a method in which the substrate is immersed in the rinse liquid for a predetermined time (dip method), and a method in which the rinse liquid is sprayed onto the surface of the substrate (spray method).

<<Polymeric Compound>>

The polymeric compound according to a third aspect of the present invention includes a structural unit (a0) represented by general formula (a0-1) shown below, a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid and a structural unit (a6) which generates acid upon exposure. The explanation of the polymeric compound of the present invention is the same as the explanation of the component (A1) of the resist composition of the present invention described above.

In the formula, R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂— containing cyclic group.

EXAMPLES

The present invention will be described more specifically with reference to the following examples, although the scope of the present invention is by no way limited by these examples.

Polymer Synthesis Example

Polymeric compounds 1 to 63 were produced using the following monomers (1) to (24) which derived the structural units constituting each polymeric compound. The polymeric compounds 1,22 and 43 were synthesized as follows, and the other polymeric compounds were synthesized by a conventional method. Polymeric compound 45 could not be polymerized. With respect to the obtained compounds, the compositional ratio (the molar ratio of the respective structural units indicated in the structural formula shown below) as determined by carbon 13 nuclear magnetic resonance spectroscopy (600MHz ¹³C-NMR; internal standard: tetramethylsilane), and the weight average molecular weight (Mw) and the molecular weight dispersity (Mw/Mn) determined by the polystyrene equivalent value as measured by GPC are shown in Tables 1 to 6.

(Polymeric Compound 1)

To a flask equipped with a thermometer, a reflux tube, a stirrer and an N₂ feeding pipe was added 36.4 g of methyl ethyl ketone in a nitrogen atmosphere, followed by elevating the internal temperature to 80° C. while stirring. Separately from the above, 16.0 g (48.1 mmol) of monomer (1), 21.2 g (80.8 mmol) of monomer (2), 6.6 g (27.8 mmol) of monomer (3) and 8.4 g (17.0 mmol) of monomer (6) were dissolved in 65.8 g of methyl ethyl ketone. Then, 2.80 g of a polymerization initiator V-601 was added and dissolved. The resulting mixed solution was dropwise added to the flask at a constant rate over 4 hours, followed by heating for 1 hour while stirring. Then, the reaction mixture was cooled to room temperature. The obtained reaction polymer solution was dropwise added to an excess amount of methanol/water mixed solution to deposit a polymer. Thereafter, the precipitated white powder was separated by filtration, followed by washing with methanol and drying under reduced pressure, thereby obtaining 35 g of a polymeric compound I as an objective compound.

(Polymeric Compound 22)

To a flask equipped with a thermometer, a reflux tube, a stirrer and an N₂ feeding pipe was added 36.4 g of methyl ethyl ketone in a nitrogen atmosphere, followed by elevating the internal temperature to 80° C. while stirring. Separately from the above, 16.0 g (48.1 mmol) of monomer (4), 21.2 g (80.8 mmol) of monomer (2), 6.6 g (27.8 mmol) of monomer (3) and 8.4 g (17.0 mmol) of monomer (6) were dissolved in 65.8 g of methyl ethyl ketone. Then, 2.80 g of a polymerization initiator V-601 was added and dissolved. The resulting mixed solution was dropwise added to the flask at a constant rate over 4 hours, followed by heating for 1 hour while stirring. Then, the reaction mixture was cooled to room temperature. The obtained reaction polymer solution was dropwise added to an excess amount of methanol/water mixed solution to deposit a polymer. Thereafter, the precipitated white powder was separated by filtration, followed by washing with methanol and drying under reduced pressure, thereby obtaining 35 g of a polymeric compound 22 as an objective compound.

(Polymeric Compound 43)

To a flask equipped with a thermometer, a reflux tube, a stirrer and an N₂ feeding pipe was added 37.6 g of methyl ethyl ketone in a nitrogen atmosphere, followed by elevating the internal temperature to 80° C. while stirring. Separately from the above, 16.0 g (50.6 mmol) of monomer (5), 22.3 g (84.9mmol) of monomer (2), 6.9 g (29.2 mmol) of monomer (3) and 8.8 g (17.9 mmol) of monomer (6) were dissolved in 68.1 g of methyl ethyl ketone. Then, 2.94 g of a polymerization initiator V-601 was added and dissolved. The resulting mixed solution was dropwise added to the flask at a constant rate over 4 hours, followed by heating for 1 hour while stirring. Then, the reaction mixture was cooled to room temperature. The obtained reaction polymer solution was dropwise added to an excess amount of methanol/water mixed solution to deposit a polymer. Thereafter, the precipitated white powder was separated by filtration, followed by washing with methanol and drying under reduced pressure, thereby obtaining 35 g of a polymeric compound 43 as an objective compound.

TABLE 1 Polymeric compound 1 2 3 4 5 6 7 8 9 10 Monomer  (1) 40 45 39 45 45 45 45 45 45 45  (2) 34 41 39 41 41 41 41 41 41 41  (3) 12  (4)  (5)  (6) 14 14 22  (7) 14  (8) 14  (9) 14 (10) 14 (11) 14 (12) 14 (13) 14 (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) Mw 11000 12000 10800 10000 9800 9900 10300 9500 10400 8900 Mw/Mn 1.75 1.71 1.74 1.74 1.77 1.74 1.71 1.79 1.79 1.74

TABLE 2 Polymeric compound 11 12 13 14 15 16 17 18 19 20 21 Monomer  (1) 45 45 45 45 45 45 45 45 45 45 45  (2) 41 41 41 41 41 41  (3)  (4)  (5)  (6) 14 14 14 14 14  (7)  (8)  (9) (10) (11) (12) (13) (14) 14 (15) 14 (16) 14 (17) 14 (18) 14 (19) 14 (20) 41 (21) 41 (22) 41 (23) 41 (24) 41 Mw 9400 11700 10500 9200 10000 12200 11800 10900 12100 12000 11500 Mw/Mn 1.75 1.72 1.73 1.71 1.72 1.72 1.72 1.74 1.77 1.73 1.7

TABLE 3 Polymeric compound 22 23 24 25 26 27 28 29 30 31 Monomer  (1)  (2) 34 41 39 41 41 41 41 41 41 41  (3) 12  (4) 40 45 39 45 45 45 45 45 45 45  (5)  (6) 14 14 22  (7) 14  (8) 14  (9) 14 (10) 14 (11) 14 (12) 14 (13) 14 (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) Mw 10800 11800 11000 9800 9900 10000 10000 9900 10000 10500 Mw/Mn 1.74 1.77 1.71 1.7 1.74 1.81 1.7 1.73 1.77 1.71

TABLE 4 Polymeric compound 32 33 34 35 36 37 38 39 40 41 42 Monomer  (1)  (2) 41 41 41 41 41 41  (3)  (4) 45 45 45 45 45 45 45 45 45 45 45  (5)  (6) 14 14 14 14 14  (7)  (8)  (9) (10) (11) (12) (13) (14) 14 (15) 14 (16) 14 (17) 14 (18) 14 (19) 14 (20) 41 (21) 41 (22) 41 (23) 41 (24) 41 Mw 9900 10000 11000 9000 10700 11800 11700 10800 12000 12500 11600 Mw/Mn 1.77 1.77 1.79 1.8 1.77 1.74 1.71 1.77 1.76 1.72 1.73

TABLE 5 Polymeric compound 43 44 45 46 47 48 49 50 51 52 Monomer  (1)  (2) 34 41 39 41 41 41 41 41 41 41  (3) 12  (4)  (5) 40 45 39 45 45 45 45 45 45 45  (6) 14 14 22  (7) 14  (8) 14  (9) 14 (10) 14 (11) 14 (12) 14 (13) 14 (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) Mw 11800 11000 Could not be 9800 11200 10000 10000 9700 11000 8800 polymerized Mw/Mn 1.77 1.75 Could not be 1.82 1.78 1.9 1.81 1.86 1.77 1.86 polymerized

TABLE 6 Polymeric compound 53 54 55 56 57 58 59 60 61 62 63 Monomer  (1)  (2) 41 41 41 41 41 41  (3)  (4)  (5) 45 45 45 45 45 45 45 45 45 45 45  (6) 14 14 14 14 14  (7)  (8)  (9) (10) (11) (12) (13) (14) 14 (15) 14 (16) 14 (17) 14 (18) 14 (19) 14 (20) 41 (21) 41 (22) 41 (23) 41 (24) 41 Mw 9200 10000 10100 9800 9200 9400 10900 11200 12500 11700 11700 Mw/Mn 1.85 1.82 1.88 1.62 1.78 1.7 1.73 1.71 1.73 1.7 1.74

TABLE 7 Component Component (A) (D) Component (S) Ex. 1 (A)-1 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 2 (A)-2 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 3 (A)-3 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 4 (A)-4 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 5 (A)-5 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 6 (A)-6 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 7 (A)-7 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 8 (A)-8 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 9 (A)-9 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 10 (A)-10 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 11 (A)-11 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 12 (A)-12 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 13 (A)-13 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 14 (A)-14 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 15 (A)-15 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 16 (A)-16 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100]

TABLE 8 Component Component (A) (D) Component (S) Ex. 17 (A)-17 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 18 (A)-18 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 19 (A)-19 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 20 (A)-20 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 21 (A)-21 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 22 (A)-22 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 23 (A)-23 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 24 (A)-24 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 25 (A)-25 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 26 (A)-26 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 27 (A)-27 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 28 (A)-28 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 29 (A)-29 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 30 (A)-30 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 31 (A)-31 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 32 (A)-32 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 33 (A)-33 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 34 (A)-34 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100]

TABLE 9 Component Component (A) (D) Component (S) Ex. 35 (A)-35 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 36 (A)-36 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 37 (A)-37 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 38 (A)-38 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 39 (A)-39 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 40 (A)-40 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 41 (A)-41 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100] Ex. 42 (A)-42 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 [100] [2.1] [1500] [1000] [2500] [100]

TABLE 10 Component Component (A) (D) Component (S) Comp. (A)-43 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 1 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-44 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 2 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-46 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 3 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-47 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 4 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-48 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 5 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-49 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 6 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-50 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 7 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-51 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 8 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-52 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 9 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-53 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 10 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-54 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 11 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-55 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 12 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-56 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 13 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-57 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 14 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-58 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 15 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-59 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 16 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-60 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 17 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-61 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 18 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-62 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 19 [100] [2.1] [1500] [1000] [2500] [100] Comp. (A)-63 (D)-1 (S)-1 (S)-2 (S)-3 (S)-4 Ex. 20 [100] [2.1] [1500] [1000] [2500] [100]

In Tables 7 to 10, the reference characters indicate the following. The values in brackets [ ] indicate the amount (in terms of parts by weight) of the component added.

(A)-1 to (A)-63: the aforementioned polymeric compounds 1 to 63

(D)-1: a compound represented by structural formula (D)-1 shown below

(S)-1: PGMEA

(S)-2: PGME

(S)-3: cyclohexanone

(S)-4: γ-butyrolactone

Using the obtained resist compositions, the following evaluations were conducted.

<Formation of Resist Pattern>

An organic anti-reflection film composition (product name: ARC29A, manufactured by Brewer Science Ltd.) was applied to a 12-inch silicon wafer using a spinner, and the composition was then baked on a hot plate at 205° C. for 60 seconds, thereby forming an organic anti-reflection film having a film thickness of 82 nm. Then, each resist composition obtained in the examples was uniformly applied to the organic anti-reflection film using a spinner, and was then prebaked (PAB) at a bake temperature indicated in Tables 11 and 12 for 60 seconds, thereby forming a resist film (film thickness: 50 nm). Subsequently, the resist film was subjected to drawing (exposure) using an electron beam lithography apparatus JBX-9300FS (manufactured by JEOL Ltd.) at an acceleration voltage of 100 kV, followed by a bake treatment (PEB) at a bake temperature indicated in Tables 9 and 10 for 60 seconds. Then, development was conducted with a 2.38wt % aqueous TMAH solution (product name: NMD-3; manufactured by Tokyo Ohka Kogyo Co., Ltd.) at 23° C. for 60 seconds.

As a result, in each of the examples, a space and line pattern (hereafter, referred to as “SL pattern”) having a space width of 100 nm and a pitch of 200 nm was formed.

[Evaluation of Sensitivity]

The optimum exposure dose Eop (μC/cm²) with which the SL pattern was formed was determined. The results are shown in Tables 11 and 12.

[Evaluation of Line Width Roughness (LWR)]

With respect to the SL pattern formed in the above <Formation of resist pattern> having a space width of 100 nm and a pitch of 200 nm, 3σ was determined as a yardstick for indicating LWR. “3σ” indicates a value of 3 times the standard deviation (σ) (i.e., 3(s)) (unit:

nm) determined by measuring the line width at 400 points in the lengthwise direction of the line using a scanning electron microscope (product name: S-9220, manufactured by Hitachi High-Technologies Corporation; acceleration voltage: 800V). The smaller this 3s value is, the lower the level of roughness of the line side walls, indicating that an SL pattern with a uniform width was obtained. The results are indicated under “LWR (nm)” in Tables 11 and 12.

TABLE 11 PAB/PEB (° C.) each Eop 60 sec (uC/cm²) LWR (nm) Ex. 1 135/110 70 7.2 Ex. 2 135/110 62 7.5 Ex. 3 135/110 56 7.0 Ex. 4 135/100 61 7.2 Ex. 5 135/100 58 7.4 Ex. 6 135/100 56 7.5 Ex. 7 135/110 72 7.8 Ex. 8 105/95  60 7.8 Ex. 9 105/90  54 7.3 Ex. 10 105/95  58 7.1 Ex. 11 135/110 64 7.4 Ex. 12 135/110 70 7.2 Ex. 13 130/100 108 7.4 Ex. 14 135/110 61 7.3 Ex. 15 135/110 78 7.0 Ex. 16 135/110 48 7.3 Ex. 17 135/110 68 7.3 Ex. 18 135/110 61 7.6 Ex. 19 135/110 55 7.0 Ex. 20 135/110 60 7.3 Ex. 21 135/100 56 7.5 Ex. 22 135/100 55 7.6 Ex. 23 135/100 70 8.0 Ex. 24 135/110 59 7.9 Ex. 25 105/95  53 7.4 Ex. 26 105/90  56 7.2 Ex. 27 105/95  62 7.6 Ex. 28 135/110 68 7.3 Ex. 29 135/110 105 7.7 Ex. 30 130/100 60 7.4 Ex. 31 135/110 76 7.1 Ex. 32 135/110 47 7.3 Ex. 33 135/105 59 6.2 Ex. 34 135/115 55 5.6 Ex. 35 120/100 55 7.1 Ex. 36 120/100 53 7.4 Ex. 37 120/100 51 7.3 Ex. 38 135/105 58 6.3 Ex. 39 135/115 54 5.7 Ex. 40 120/100 54 7.2 Ex. 41 120/100 52 7.5 Ex. 42 120/100 50 7.4

TABLE 12 PAB/PEB (° C.) each Eop 60 sec (uC/cm²) LWR (nm) Comp. Ex. 1 135/110 60 8.9 Comp. Ex. 2 135/110 55 9.3 Comp. Ex. 3 135/100 55 9.7 Comp. Ex. 4 135/100 50 10.1 Comp. Ex. 5 135/100 49 10.5 Comp. Ex. 6 135/110 65 9.9 Comp. Ex. 7 105/95  53 9.4 Comp. Ex. 8 105/90  49 9.4 Comp. Ex. 9 105/95  51 10.5 Comp. Ex. 10 135/110 57 11.9 Comp. Ex. 11 135/110 61 10.8 Comp. Ex. 12 130/100 94 9.3 Comp. Ex. 13 135/110 55 9.0 Comp. Ex. 14 135/110 68 9.6 Comp. Ex. 15 135/110 43 9.3 Comp. Ex. 16 135/110 54 9.7 Comp. Ex. 17 135/105 49 8.7 Comp. Ex. 18 135/115 46 8.9 Comp. Ex. 19 120/100 46 8.8 Comp. Ex. 20 120/100 44 9.2

As seen from the results shown above, the resist compositions of Examples 1 to 42 exhibited excellent lithography properties such as LWR, as compared to the resist compositions of Comparative Examples 1 to 20.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 

What is claimed is:
 1. A resist composition comprising a base component (A) which generates acid upon exposure and exhibits changed solubility in a developing solution under the action of acid, the base component (A) comprising a polymeric compound (A1) comprising a structural unit (a0) represented by general formula (a0-1) shown below, a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid and a structural unit (a6) which generates acid upon exposure:

wherein R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, —CONH— or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂— containing cyclic group.
 2. The resist composition according to claim 1, wherein R² is represented by general formula (3-1) shown below:

wherein A′ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; a represents an integer of 0 to 2; and R⁸ represents an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyl group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group.
 3. The resist composition according to claim 1, wherein the structural unit (a6) has a group represented by general formula (a6-0-1) or (a6-0-2) shown below:

wherein Q¹ and Q² each independently represents a single bond or a divalent linking group; R³, R⁴ and R⁵ each independently represents an organic group, provided that R⁴ and R⁵ may be mutually bonded to form a ring with the sulfur atom in the formula; V⁻ represent a counteranion; A⁻ represents an organic group containing an anion; and M^(m+) represents an organic cation having a valency of m, wherein m represents an integer of 1 to
 3. 4. A method of forming a resist pattern, comprising: using a resist composition of claim 1 to form a resist film on a substrate; conducting exposure of the resist film; and developing the resist film to form a resist pattern.
 5. A polymeric compound comprising a structural unit (a0) represented by general formula (a0-1) shown below, a structural unit (a1)) containing an acid decomposable group which exhibits increased polarity by the action of acid and a structural unit (a6) which generates acid upon exposure:

wherein R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, —CONH— or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂— containing cyclic group.
 6. The polymeric compound according to claim 5, wherein R² is represented by general formula (3-1) shown below:

wherein A′ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; a represents an integer of 0 to 2; and R⁸ represents an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyl group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group.
 7. The polymeric compound according to claim 5, wherein the structural unit (a6) has a group represented by general formula (a6-0-1) or (a6-0-2) shown below:

wherein Q¹ and Q² each independently represents a single bond or a divalent linking group; R³, R⁴ and R⁵ each independently represents an organic group, provided that R⁴ and R⁵ may be mutually bonded to form a ring with the sulfur atom in the formula; V⁻ represent a counteranion; A⁻ represents an organic group containing an anion; and M^(m+) represents an organic cation having a valency of m, wherein m represents an integer of 1 to
 3. 